I've had a couple people in the notes wondering about build costs and process for the aviary/catio section. It's made of treated lumber, which is not cheap in an already not-cheap lumber market; the addition cost me about $150 in wood. I could have built it a little cheaper, but I made some stylistic choices that cost me some extra board footage.
It's painted with black exterior paint (already had it from painting my house) and uses a coated wire 2x3" fencing, with a salvaged door. I spent a couple bucks on hinges and latches, and a few more on decking screws and washers (to help tack down the fencing). Smaller fencing is advisable if you have predators or aggressive strays in the area. I'm in an urban enough location that I'm not really worried about it.
If you're building a catio, the shape I chose is not the most efficient. It mirrors the shape of the aviary, which has an eight-foot internal peak, and is six feet wide. Standard board lengths come in 8 feet, so it's more efficient to design in increments of 2, 4, or 8, and choosing to do an angled roofline adds height that doesn't really do anything for Malice. She doesn't want to go up there and I'd hate to have to pull her down from that high when it's time to go indoors. It's also helpful to figure out what width of fencing you're going to be using, and design around that dimension--you'll save a loooot of snipping that way.
The salvaged door is something I would recommend though! It's nice to be able to enter easily, and old doors with broken glass are very easy to find; I just built the door frame about an inch bigger than the door dimensions, broke out all the broken glass, painted it, and attached fencing where the door used to be. I don't bother with the door latch, I just use a hook and eye set.
Theoretically you can build this whole thing using hand tools, but power tools make it much faster and easier. If you can find a drill, circular saw (or, ideally, a compound miter saw, aka my favorite), tin snips, and staple gun, you can build this in an afternoon. Painting it will take a little longer, and it's easier to paint it before the fencing is attached. It's also something that can be built with only one set of hands, because the whole thing is relatively lightweight, since it has no solid walls. And catios in general are a pretty good beginner project, because they don't need to be significantly weight-bearing.
