I found an old playpen at a garage sale one year. I brought it home, and we placed chicken wire around it, and hubby made a nice screen top for the roof- he framed it and attached it. I use that when my sick ones need sunshine- or i have baby kitties that I want to go outside for awhile to introduce them to the rest of the crew safely. But whatever you use, you need to introduce your cat to it gradually, because to have a freaked out cat inside a wire enclosure is pretty scary. I used the smallest wire openings available for chicken wire, but still, a freaked cat will try and get their head out of any opening they can. Unlike us, they don't have a collarbone, so if they can get their head through, they can get the rest of their body through it as well.