We recently got a cat for our family and I thought she'd appreciate a treehouse in her favourite tree. The size of the treehouse can easily be changed, I settled on this size due to the scraps of timber I had on hand.

Supplies

Cat to supervise the building
Plywood (treated)
Other timber, 25mm x 25mm (can be trimmed down from 2" x 4")
2" x 4" treated timber
Screws (galvanised or stainless steel)
Drill
Handsaw or circular saw
Jigsaw
Scew Driver
Tape Measure
Paint
Woodglue
Paint Brush
Steel Roof Flashing (optional)
Sandpaper
A Tree
Spirit Level

Step 1: Cut Out the Parts

I used 12mm thick plywood and the measurements are designed for 12mm overlaps. Now use a handsaw or circular saw to cut all the pieces out. Use a compass to draw the semi-circle at the top of the doorway, then use a jigsaw to cut the hole out.

I didn't have any spare pieces of wood 25mm x 25mm, so I just ripped a spare 2"x4" down with the circular saw. I then trimmed each of the supports down to the appropriate length.

Step 2: Predrill the Holes

I then marked and drilled the holes through the plywood for the screws. The hole needs to be a little bigger than the screw thread, this allows the plywood to pull tight on the supports.

It's very important that your cat supervise you during this stage to ensure quality control.

Step 3: Assemble the Parts

If you look at the attached image you can see how the Cat Treehouse goes together. The supports are used to screw into, it's a good idea to apply some wood glue before screwing everything together.

While not required you can add some roof flashing along the top of the roof, I had some spare so cut it to length and screwed it on with roofing screws. Roofing screws have a rubber washer to prevent leaks.

Step 4: Painting

I primed the plywood with exterior wood paint, and then I recruited my Daughter to pick some colours and paint the sides. And of course, we had to write her name on the treehouse.

Step 5: Put It in the Tree

Once you find a good place in the tree you need to add some supports for the treehouse to sit on. I ran a couple of 2" x 4"s across some branches, I used a spirit level on each of the supports to keep things level. Now use a few really long screws to hold the supports onto the tree.

You can now sit the Treehouse onto the 2x4 supports and screw it into place.

Lastly, I added a small ramp from an offcut of plywood down to the nearest branch of the tree.