The Cat Carpenter Kirby's Window Catio
I was originally thinking wrap around, but they're really going to want to be on the sunny side, and they'd love multi-story. Maybe it could go on one of the sides, but all the way to the front? The whole thing doesn't need to be sheltered from the elements, but we'd need at least a low liftable roof over the cat boxes. Getting them out of the small space is one of the goals.