With several cats in the house, we've wanted (for quite some time) to get them a unique play spot/area/thing, and wondered about those multi-level scratch towers that you see in pet stores and online. There are tons of designs and layouts, and building one instead of just buying it was always a criteria.

The towers, however, all had the same issue for us: where to put one? We wanted it to be tall enough so the cats could walk/jump to the very top, that it should [hopefully] reach the ceiling, and also be in a spot that doesn't take away from the room. The towers do have quite a foot print (we figured at least 2.5 square feet), so it was a concern.

While wondering about this we also realized that we had an under-used closet area underneath our basement staircase. Over the years it ended up just being a dumping spot for old toys, storage bins, etc. Re-purposing the closet as a "built-in" cat tower would save us the floor space needed for this, and provide an excellent opportunity to de-clutter, so off we went!

Step 1: Planning and Materials

Sketchup was the tool of choice for the design step, especially since they have a free version offered online (https://www.sketchup.com/products/sketchup-free). There are plenty of good tutorials and videos online on how to use that tool, so I won't go though that here. The basic steps, though, were to take measurements of the inside of the closet, use them to create a new project area, and then just play around with different layout ideas.

For the requirements - we knew we wanted to have several floors, have plenty of scratching surfaces, easy access from one floor to the next, and hopefully a good way to keep the littler box and food in there as well while having an easy way to maintain and clean the place. Because of the layout of the closet, some of the floors would end up being quite deep so we also wanted to ensure easy access to the back of the closet (for cleanup).

The materials were pretty straight forward; we weren't trying to over-engineer the project, so using up any scraps we had on hand was a definite possibility. I opted for using 0.5" OSB (Oriented Strand Board) as the material of choice for the shelves because it's relatively strong, cheap (a 4' by 8' board costs around $12) and can be easily re-enforced from the bottom with strips of wood cut out of 2 by 4 beams (for long sections that start having a bit of bow in them). This project needed two 4'x8' boards.

Carpeting: I looked around quite a bit for ideas, and considered using a second hand carpet that I could cut up into sections, but I was concerned about fraying along the edges and the actual aesthetics of having random parts of the original carpet's design show up around the shelves. In the end, I found a carpet runner that was sold by the linear foot and was 26" wide. The runner was on sale for a bit over $2 a foot, and 30' of the material did the job.

The only other purchases we needed to make were hinges to attach the ramps (abut $4 for a pair, and we needed two) and plastic casters for the roll-out shelf the litter box would go on (about $2 each). Each of the casters is rated for about 40lbs, so all together they were more than enough to hold up the shelf, bin and cats.

Tool-wise, having a table saw really helped here but the cutting does not have to be 100% precise since the edges will end up covered by the carpeting, so you could definitely do with a circular saw or even a jigsaw (OSB cuts extremely easily). You'll also need a drill and impact driver, glue and a staple gun with 3/8" staples (for attaching the carpeting to the shelves).

Step 2: Preparing the Closet and Cutting the Shelves

Prep is pretty straight forward: empty the closet and clean it up.

The first step is installing the cleats, long horizontal strips of wood attached to the wall upon which the shelves will sit. As far as permanent attachments are concerned, the only ones in this project are between the cleats and the walls. The shelves just sit on the cleats and stay there under their own weight.

To attach the cleats, use a stud finder to locate the studs in the wall, and ensure you screw right into them. I used left over 2x2 beams for the cleats and was concerned about splitting while putting the screws through them, so opted to pre-drill them.

Once the cleats are on, move on to cutting the shelves to size. I had the boards pre-cut at the store to a size slightly larger than the final dimensions (for easier transportation and to be able to fine-tune the cuts at home through fitting trials). It's important at this stage to keep future maintenance in mind, so think about how you'll get to the back of the closet for cleaning. If any of the shelves are too deep (such as the first and second ones in our case), consider making the shelves in two (or more) sections that you can lift out of place independently, and leaving a gap between those sections to accommodate the carpeting material that will wrap around each section (I left about 0.5").

When you've got the shelves cut to size, it's time to mark the locations of the openings for the ramps and cut the ramps themselves. In our case, I knew I wanted the openings 6" away from the wall but was not sure how long they would need to be, so started small to be safe. The initial size of the openings was 6" by 12", and after cutting them and dry fitting the shelves I had the cats play in the closet for a while to see what they thought. It looked a bit tight at times, so I ended up with 6" by 18" openings instead.

Step 3: Reinforcements

The OSB board is sturdy enough in small sections, but at a width of 2' or so you can start seeing a definite "give" when you press in the middle; try positioning it on two objects spaced apart as wide as the board is, and press in the middle to see how flexible it is. To solve this, I needed wooden runners attached in both directions, but the job was cut in half by realizing that the cleats on the wall would also act as runners, so I just needed additional ones going in the perpendicular sense (i.e. from wall to wall).

The runners are made from simple 1x2 strips, and I had extra 2x2 and 2x4 pieces lying around that I just ripped to the size on the table saw. Once they were ready, I glued them to the underside of the shelves and ramps, clamped them in the place, flipped the whole thing over and screwed them in from the top. Attaching the screws from the top has the advantage of hiding the screw heads underneath the carpet.

In addition to the runners, a small piece was also needed at the top of the ramp as well as near the start of the hole in the corresponding shelves in order to later attach the hinges (since the OSB is too thin and will not hold the screws very well on its own).

Step 4: Litter Box Tray

The litter box level is composed of two parts: the tray that holds the litter box, which has raised lips to catch any litter being kicked out of the box and is mounted on casters for easy moving in and out of the closet (in order to clean the litter box), and surrounding "filler" platforms that are the height of the raised tray's lips. The whole look ends up being that of a large shelf area with a sunken front/center section, upon which the litter box sits. When a cleaning is called for, you just roll that center/front section out of the closet, deal with the cleaning, and roll it back. Simple.

The tray starts out as any of the other shelves have, by having the support slats attached to the underside edges with glue and screws, but this time the slats cover all four sides since there's nothing else there to hold them up. When this is complete, four additional pieces of OSB are attached to the sides of the tray to form the skirt. The skirt is basically tall enough to protrude 0.5" above the height of the tray, and reach within 0.5" of the very bottom of the casters. This has the effect of creating a top lip to contain spilled litter, and is raised slightly above the floor to prevent scratching when the tray is rolled around.

For consistent attachment height, I put the tray upside down on a two scrap pieces of OSB (basically lifting it 0.5" off the work surface), and glued/screwed the skirts sections to the edges of the tray while making sure the skirt was actually touching the work surface. The skirt corners were also glued to each other, but here I used finishing nails instead of screws to avoid blowing the board apart. When the skirt was complete, the casters were attached to the wooden slats at each corner while ensuring they had enough clearance to swing free of the skirt.

Surrounding the tray are three additional sections that are as high as the top edge of the tray's lips, and they're extremely straight forward: the reinforcement strips are added underneath them, but those strips are pilled up until the necessary overall height is achieved. Also, the slats are needed the full length of these sections where they meet up with the central tray so as to not leave a gap when the tray is moved out, but in the back (where those sections meet the wall) only a couple of pieces are needed for support (I added them in the corners only, and it was more than enough to support the cats' weight).

Step 5: Cutting and Attaching the Ramps

The ramps, with the support slats attached, have a 90° edge on both the top and bottom, which makes attaching them to their shelf and lying flat on the shelf below pretty challenging. To get around this, I cut the corner off to match the angle, and used a quick diagram like the one attached here.

Starting off with the overall measurement of the opening angle being at 145° (A) (yes, I'm rounding the values, but the difference is minor and is not noticeable), I can bring a line straight down from the middle of that angle, dividing it in two angles, 90° (B) and the remainder of 55° (C). Since the ramp is parallel to the left side of the protractor, bringing down another vertical line from the corner of the ramp downwards gives me angle (D) which matches angle (C) at 55°. And knowing that the full angle of the ramp's corner is 90°, subtracting angle (D) from it gives me 35° (E), the angle I need to remove.

Once that corner is cut off, follow the same mechanism with bottom of the ramp to make it flat with the lower shelf, cut that corner off, and we're done with all the cutting. Time for a dry fit of everything and making any last minute adjustments to ensure everything works.

The final step, after both ends of the ramp have been cut at the proper angles, is to join the ramp and shelf with a hinge. The ramp will never really swing from the shelf, but using a hinge gives the flexibility of attaching something at unconventional angles.

Step 6: Painting, Carpeting and Final Setup

Now that everything is cut out and the dry fit is tried out again, it's time to remove everything one last time and get the surfaces painted. The walls of the closet, the undersides of all the shelves and the top surfaces of the litter tray (and accompanying filler sections) were given two coats of a highly washable latex paint.

When that was done, it was time for the carpet installation. All the shelves and ramps went through pretty much the same process for this: starting underneath the shelf, I attached the carpet to the runner with staples. For stapling in general, start in the middle of the piece being attached and work your way outwards; this helps ensure no fabric "waves" are caught in the middle.

With one end stapled, the shelf was inverted, pulling the carpet along. The carpet was then wrapped tightly around the opposite side of the shelf and stapled to the second runner. If the shelf was also a front one with a raised edge, the carpet was then stapled to the inside of that lip to keep it all tight. Extra strips were then cut and stapled in the same manner on the sides of the shelf, to cover the areas that were beyond the full width of the carpet runner.

If the shelf had an opening for a ramp, the hole was cut from underneath in the shape of an "X", and the resulting triangles were folded tightly and stapled to the underside of the shelf.

Step 7: Final Look and Thoughts

And that was it. The project took a couple of weeks to complete, but was well worth it. The kitties love it, and I have enough carpeting material left over to make a couple of extra things, such as a short 2' tunnel made out of tough cardboard roll covered in carpeting.

Cleanup of the littler appears pretty straight forward, and being able to easily slide the litter tray in and out of place is awesome. There's obviously some litter that's getting thrown around by the furballs, but it's easily swept up or vacuumed.

I hope this instructable ends up being useful out there and generates some good ideas. If you follow any of it and build something like this, leave me a comment with some photos!