I recently designed a cat tree for our cats in Google SketchUp.
You can download the whole model at the SketchUp 3D Warehouse [link].
With the help of Aryeh, last Saturday night we cut up various pieces of lumber for the project.
Then I borrowed our building's superintendent's power screwdriver and put the thing together:
Although I haven't carpeted it, completed the little house on bottom, or wrapped the posts in sisal rope, the kittens still like it:
The shirts draped on it are to make it slightly more comfy for the cats before I get a chance to carpet it.