So how much of the existing armoire structure are you willing to cut out? I'd want to cut panels out of the sides and replace panels with screen. Otherwise its going to be pretty closed in (air flow, overheating from lights) and dark (even with lighting). The wood will warp and rot if you don't seal all the wood very well. Several forum members have built drains into furniture bases. One that seemed easy included installing a false bottom...creating sloped panels (sealed wood with coroplast glued on top) on top of the original flat bottom that all lead to one drain point in the center. The slope doesn't have to be extreme. Installed a pvc drain fixture, pvc pool tubing that lead to a bucket underneath.
Years ago I saw a fantastic screen cage made out of a large old school library bookshelf in Reptiles magazine. Floor to ceiling, arched scrolled top and carved frame, but all the sides were screened in. It was beautiful.