Spray paint should be fine when dry, but your going to want to go over it with a clear coat anyway to make it moisture proof. Just make sure you allow plenty of time for it to cure before putting the animal inside. Usually my rule of thumb is if I leave the cage sealed up for an hour and can still smell the coating when opened, then it need more time. also make sure your coatings are all compatible. In my case I just use a green stain on the plywood and then clear coat it with polycrylic. Depends on the material too though.
