I have been building again. removed the old pitiful shop bought cat playground, and built what i call Cat Shelves :)
Each cube is 40cm squared. There are holes to go up, down, and a bit of a maze to get to the top.
I made 3 dead end boxes for beds which have blankets in them until i get pillows (and will get a front panel) and a couple of larger double sized areas for them to play in.
The whole thing was made with 12mm hardwood ply (non-treated), and took 2.5 sheets (2400x1200mm).
Took about 2-3 hours work, and about 10 hours planning (at the least!)