My post about
why a DIY aviary is generally a bad idea. Of course if you have access to welding equipment, materials, powder coat facility, a lot of time, and the will to do it, go right ahead. Otherwise, from once contemplating this same issue myself, I found that the cost of entry to get involved with doing it myself and doing it well, would cost as much or more and a ton of time on top. Of course,
the aviary I ended up buying was a disaster that I would not wish upon my enemies, however, I know others have had success with alternate brands so there must be something out there. So while I think people can save money and even do a better job when it comes to DIY like toys, special foods, and play stands, I just don't see it with aviaries.
Maybe you live in a location where there simply is not a supplier of aviaries nor the ability to hire a professional. Then you'd be forced to do it yourself not by choice. But be prepared for it to cost a lot and be an insane amount of work to do it right.
One recommendation I would put forward no matter what design, is to build a double aviary if you have predators around (foxes, racoons, cats, hawks, owls, etc). I know so many cases of birds grabbed through the bars. Even if they aren't pulled out, still killed inside. Ideally you should build an aviary within an aviary (you can use cheap chicken wire or whatever on the outside since the parrots won't come into contact with it). Also burying the wire walls deep down underground and burying a wire floor on the inside should help against borrowing animals if you don't put it on a concrete slab. Final piece of advice is if it's not a full time habitat, don't get any food stations and don't ever provide food in the aviary. Aviary should be just for playtime and no eating. No food means you reduce the amount of pests and things trying to get in there. Then you just have to worry about the things that find the inhabitants to be the food.