Amazing Tee Houses - you can DO this!
For Cat lovers- 27 Useful DIY Solutions For Hiding The Litter Box
Cat walk - easy to recreate with floating shelves, boards and simple hardware. Hours of kitty fun!
Convert a book case into a cat tree... Soo cool!
An entire blog on Cat Ladders! #cats #CatStairs
Make Your Own Cat Trees, Towers, and other DIY Cat Structures
DIY Cat fun: 10' tall climbing post fashioned from a 2x3 wrapped in cotton clothesline rope.
DIY Cat Tree from A-Frame Bookshelves
6 Free Plans For Amazing Cat Trees
DIY Cat Climbing Tree, with link to construction pictures