We made a frame out of 1x4's then layed the 1/2 plywood floor on top of the frame and screwed them together, up from the bottom and into the screendoor frames. The doors are sitting on top of the floor, (that way the floor supports their weight and I believe it helps prevent the dust from sifting out onto the floor). The doors are then fastened together with L- brackets like this at the corners,

and flat brackets like this along the front,
I only used four screen doors... one for each end and two along the front. I then used plywood for my back wall and top.
It looks like you have six doors. If your aviary is going to be more than 6' long I would brace the floor. We didn't mine as it is only 6' and it supports me, I weigh 140lbs. It is sitting on 2" casters.
Keep in mind that I used plexi glass for the bottom half of mine, this REALLY helps to contain the mess. It was rather expensive but WELL WORTH IT.
If you have any other questions I would be happy to tell you what we did. My brother is very good at woodworking so he made me small access doors at each end, top & bottom. This is something you might want to think about doing also as it prevents birds from escaping. I can take some photos later if that would help you.
TammieB.
Use the talents you possess - for the woods would be a very silent place if no birds sang except for the best. ~Henry Van Dyke~