This cat box design eliminates litter mess on the floor, by encouraging the cat to climb up a sisal ramp to exit. It keeps all of the litter contained and because the lid lifts up, it makes cleaning the area very easy. Basically, it's just a deck box with a regular litter pan inside it, and a sisal ramp to get the cat's paws clean on the way out.

As a cat owner, I'm surprised that they don't already mass-produce a product like this. Everyone who owns cats knows about the problem of litter kicked out of regular cat boxes and tracked around on cat paws. I put expensive litter mats in front of my regular covered cat boxes, but my cats just jump right over them. By putting their pan inside of a larger box, with the exit up high, where litter can't get kicked out, and by providing the sisal ramp to clean the cat's paws, my floor stays spotless.

Tools:
Magic Marker
Hot Cutting Tool (or hacksaw or other plastic cutting device)
Pencil
Hand Saw
Electric Screw Driver
Square or Straightedge
Scissors

Materials:
1x Regular Cat Litter Box
1x Plastic Deck Box
1x 1" x 6" board (actual width will depend on the hole you cut)
2x Metal L-brackets
4x 1/2" screws
100ft Natural Sisal Rope (1/4" thickness)
1x bottle Carpenter's Wood Glue (fast drying 30min)
1x roll of Plastic Tape

Step 1: Make a Hole.

Sketch out an opening big enough for your cats on the upper part of one of the end pieces. Avoid the support braces, wherever possible.

Use a Hot Cutting Tool (or hacksaw or other plastic cutting device) to cut out the opening. If you use a hot tool, do the cutting outdoors because there will be strong fumes. If you cut using a saw, make sure to file or otherwise round the edges so the plastic is not sharp.

Step 2: Size the Ramp.

Assemble the bottom part of the box, but leave the lid off to make working with it easier.

Set the cat litter box that you will be using in the end of the box opposite from the entry hole that you cut.

Stick the ramp board through the hole so that it ends just outside of the litter box. Mark the length with a pencil, then remove the board and write on it so you will remember which side is for the box and which side is scrap.

Use a straightedge or carpenter's square to straighten up the pencil mark. It's best to err on the side of a shorter ramp, so you can see I marked the straightened line toward the box side of my board.

Saw the board along the line. This works best if you saw a bit from both sides. If you start on one side and saw all the way through, there will be splitting on the bottom of the board. You can see in the photo, because I sawed from both sides, the splitting happened in the middle of the board and it cleaned up nicely.

Set or hold the ramp in place in the box, and line up the L-brackets so they will hold it up.

Screw the L-brackets to the wood ramp, but not to the box. They will simply slip over the edge of the plastic, so the ramp is removable for cleaning underneath. (Removable ramp = very important feature for cleanliness.)

Step 3: Wrap the Sisal.

Starting at the under side of the end with the brackets, glue down the end of the sisal about 3/4 inch from the end of the board and wait for it to dry.

After the end of the sisal is attached firmly, add more glue. Wrap the sisal tightly around the board, working toward the end with the brackets first. After you get to the end of the board, cross over the wrapping that you have done on the under side of the board, leaving the top side of the board smooth.

Continue wrapping the sisal as tightly as possible, using glue on the under side of the board only, and making sure that the top side of the board remains smoothly wrapped. I glued in three lines for most of the board, but added some heavily glued anchoring areas every six inches or so.

When you get to the bottom end of the ramp, loosely wrap the sisal in loops over the end of the board to estimate how much sisal you will need to finish. Cut off the excess, to make working easier.

Now's the tricky part. Slop a whole bunch of glue all over the end of the board, spiral the sisal inward in loops to cover the end, and hold it in place with your hands until the glue begins to set up (this is why the quick-drying glue is best for this project).

Trim off any extra tail of sisal, tuck the end in, and glue it down well. You can also go back to the beginning and glue down anything that seems loose, but be sure to keep the glue on the under side of the ramp as much as possible. You want the top side to be loose, so the sisal will wiggle a little under the cat's paws and help clean them.

Let the whole thing dry for at least a couple of hours before you let your cats near it, because they will instantly know that it's for scratching and they'll tear it up if the glue is not dry.

Step 4: Seal the Cracks.

Instructables comes in really handy for you right now... You can learn from my mistake, so you won't make it yourself. My first instinct was to seal the crack around the bottom of the box with caulk. This turned out to be a BAD IDEA, because the bottom of the box is a separate piece that sits on a lip of plastic.

The caulk just oozes down into the crack and out of the bottom of the box onto the floor! If you are a caulk expert or know of some other product to seal the crack without making a mess, by all means add a comment.

My solution was to use plastic tape instead of caulk. Basically, I just want to keep litter from getting stuck in the cracks around the edge of the floor.

To get the tape to lay flat, I had to lay it in place, and then snip the tape on each side of the ridges in the sides of the plastic box. This left tiny places that are not sealed, but it does serve the purpose of keeping most of the loose litter out of the cracks.

I guess one clear advantage of tape over caulk is that if I ever need to move, I can take the box apart easily and just retape it whenever I set it back up.

Step 5: Assemble.

Put the ramp in place.

Set the filled litter box inside.

Put the lid on last.

Introduce your cats by putting them one at a time into the box and closing the lid. After they find their way out, they will easily be able to find their way in again.

If you need to, you can place a ramp near the entry hole on the outside, to make entry easier. My cats have no trouble getting in all by themselves. As a matter of fact, they played with it the whole time I was building it.