Since the floor was already ceramic tiled and the grout was water sealed we just caulked with silicone around the base of the frame inside and out. This keeps any water or seed from getting in or under. I put down care fresh natural bedding. With housing just one breeding pair of parrot finches and their chicks for a short time I only vacuum it out about once a month. I recycle it to the compost barrels. I then can wipe down, mop and replace the bedding. I love the care fresh product. even after the birds splash their bath water it absorbs and dries out without odor. It absorbs bird droppings and stays looking nice. The parrot finches even pick out pieces and incorporate them into thier nest
I plan on resting this pair soon and will probably put some gouldians in it for a change

What are you walls made of? Sheetrock? If you install green board you could tile and use a curved tile along the bottom, somewhat like a shower stall. If it is sheetrock whatever you use make sure to seal with a silicone product to prevent any moisture that could cause mold and mildew.