This link has been around for a while. Very nice cage and well documented build. Hope it helps.
It was made with melamine. I personally would prefer oak wood or birch plywood and use an all natural stain or paint it. Melamine can chip easily. The interior to that is easily to change. If you make it larger just ajust the blueprint for size is all. Wood sheets are 4x2 4x4 or 4x8 typically. Most hardware stores will cut wood for free or a small sheet. Lowes and home depot will do 2 cuts per board free