What a neat idea. I haven't seen anything like that before. I wonder if it is something you would have to have custom made.

My cats are evil geniuses, so I think I would fear their inevitable escape.

That's one thing I really want to do somehow-- in the most cost-effective. I've seen some directions on making one with 2x4's and chicken wire and a cat door on a window. That should be relatively cheap for a short term solution. I want to plant nontoxic stuff in it that they'll like-some herbs, cat grass, lemon grass, maybe mint. I would love to see some pics and get more ideas if someone has some.