i dont know what your hard on with aluminum is, but all you need is untreated wood, two hinges for a door, and screen small enough so your feeders dont escape.
Well, I can tell you from experience that untreated wood warps and rots pretty quickly.
I took quite a bit of time once and built about 20 nice wood cages, painted them with exterior house paint, and they didn't warp too badly once painted, but they did rot out pretty fast (like 4 or 5 years which sort of sounds like a long time, but when they start going bad at roughtly the same time it seems like a very short time to have to invest more time and $$ to redo everything) being exposed to misting systems, humidity, rain and weather. The problem was the surfaces where the wood touched wood- like at the corners and around the solid bottom.
If I was going to do wood frames again myself, I'd paint all the parts before assembly, then paint again after, and then seal the seams where the parts touched each other after assembly with some sort of waterproof adhesive- maybe silicone, maybe liquid nails or something else. I would also paint over the staples once the screen was attached as well. All of these places had rot begin.
I would also not use a solid bottom. (In my situation where the cages are not in my living room) Last time I used a solid bottom with a hole for a drain, so it could support the weight of a large potted plant. the bottoms eventually weakened considerably from rot. I would use rubber coated hardware cloth (the green stuff often used for rabbit cages), and I would then cover that with a layer of screening as well, to keep insects in, yet provide enough strength to hold heavy potted plants.
The other weakness in this type of cage is a door that doesn't allow the feeders to escape around it's edges. It's pretty hard to get a door tight enough to prevent feeders from just walking out around the door frame, and even more difficult to get a wooden door and frame that won't warp pretty quickly out in the weather so that it remains feeder escape proof, even if you are lucky (or skilled) enough to get one that starts off that way.
The type of aluminum window framing that they sell in the US is pretty cheap too- pretty similar to wood framing in cost I *think*. Aluminium framing is just as easy to work with, and doesn't warp or rot either...
I'm actually looking at all this stuff right now too, because I've got about a zillion new cages to make for this summer season, and it's coming up on us pretty quickly now...
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