After a whirlwind cat-colony project, two work trips, and lots of back-and-forth from veterinarians and spay/neuter clinics, I finally blew the dust off my personal computer, pulled it out of the "cold room" (it's too warm for the woodstove, but too chilly to have the whole house open) and set it up next to my work computer to let the world know we are still alive out here in Spencer NY.
A catio post came across my Facebook news feed today (Thank you to the personal Facebook page of Peter Wolf of Vox Felina). You can see some great catios here.
Here's some 2011 video of kittens on our catio:
My catio has been a lifesaver for me. Back in my wildlife control days, I won a huge bird rehabilitation cage at the New York State Wildlife Rehabilitation Council conference. I strapped it (un-assembled) onto the roof of my truck cap, and hauled it home. I then dragged it along (still un-assembled) when we moved from West Danby to here in Spencer. Finally, I hauled it out and with much cursing, made a catio out of it. Sooner or later it will need to be replaced, since it's just stained pine, but in the meantime the cats can go outside through a window in my pantry, winter or summer.
I recently saw a post, which I cannot find, of how one might make a small window catio out of small wire dog crate. I may do that upstairs.
What I would recommend in a catio if it is going to be open day and night:
Hardware cloth. Wildlife can squeeze through 1X2 wire, and a weasel can even get through 1x1 wire. Hardware cloth will also deter (but not completely ban) larger insects like moths.
A cat door instead of leaving a window or patio door wide open to the catio. This will keep mosquitos and moths from coming into your house at night and also keeps your house a bit warmer (or cooler) when weather is extreme. They come in patio door sizes as well.
A LOCKABLE human-sized door for outside access, if you don't have door access from the inside of your house. Padlock your latch. This is just common sense. You never know when a raccoon might fiddle with it, or a neighborhood kid might think it's "funny" to open the door. There is also simple human error. Even an unlocked padlock run through the holes in the latch will prevent accidents. Then be sure to lock it when you are not at home.
A roof, whenever possible. I know lots of catios show sides that are angled in to keep cats inside, but that doesn't keep other animals out, nor keep birds out of cat food and water bowls. If you have a very large catio, you might want to use a Purrfect Fence type enclosure, or protect both sides with coyote rollers, but I wouldn't suggest allowing your cats unsupervised night-time access.
Inspect your catio regularly, especially if it is made of wood and wire or mesh. Wood warps. Staples rust or pop out. Mesh gets torn. Even wire gets weak spots. Recently I discovered my outdoor cat Buster was climbing up the outside of the catio and sleeping on the roof like a hammock. The roof material was thick but soft plastic mesh. It occurred to me a raccoon could rip through that mesh like butter, so I added a layer of chicken wire until I can build a real wood-and-shingle roof.
A Google Image search of "catio" can waste your whole morning with dreaming, but if you are considering a catio, I highly recommend looking online to see what everyone else has done!