Oh, have the doors as sliding glass, way easier. Get a good sealer too. I just got done making two brand spankin new cages myself.

Cost me:
16$ for sealer
30$ for plywood
25$ for glass
15$ for 1x2's and all.
Paint brushes...

I probly screwed it up a bit, but it was something like that. I had screws and tools all handy, plus I had the glass for one cage.

That was for two cages mind you, not one. They were 39x22x22. Try and go simple, the simpler the better.