You know, most feed supply stores carry cage wire you can buy. They have some that is 1/2" wide by 2" long rectangles, and only the smallest babies could squeeze through that. It comes in 24" wide and 36" wide rolls. Most places will sell it to you by the foot, and it's fairly reasonable.

I bred birds for years, and believe me building my own cages was the way to go. You can also buy what they call "J" clips and spring loaded pliers for crimping them to the wire. You could easily cut the wire into panels, flatten them out a little, them crimp them loosely enough that you could fold it flat when not in use.

Gale