Hello. I am joining mainly to show a few pictures of a cat condo I just built for a young friend of mine and the four un-neutered male cats in her house (yes, I keep telling her to neuter them) to give ideas to anyone who might want to build such a thing themselves. OK, fine - it's really just to show it off.
The base is 2'x4' plywood with two 7' wood posts glued and screwed to it with 1/4"x3-1/2" SPAX PowerLags, and everything else similarly attached to this skeleton with metal L-joints, wood posts, glue, wood screws, and PowerLags. All posts are solid wood covered by sisal rope from U-Haul. The big platforms are 2'x2' plywood, and are not quite level due to the way I cut off the ends of the supporting posts. The secondary platforms are level. The tube is a 2' length of a 12" concrete footing form. All covered in carpet. There are numerous brass eye hooks attached to the bottom for dangling toys.
I thought of lopping off the pointy tips and putting a couple of perches up there, but I really like the way the points look. Since the tips almost scraped the ceiling where it was installed (not in the house in the pictures), it's best I left them alone.
The girl I made it for wanted it all tan (ugh). I decided to break it up with some grey carpeting.
My own cat (18yo female tabby), who can slowly get up and down stairs, showed no interest in it. When presenting this thing to the four cats they were all over it immediately. I found it helped to rub some catnip into the carpeting.