Here's an example of a sunning enclosure that I built. Its for lizards or torts, but you get the idea. I usually partially cover the top with a piece of plywood, but I took it out for the photo. The 12" high border around the bottom keeps them from rubbing their snouts on the wire or trying to escape. I hose the substrate first to try to keep it more humid. It abut 3x8'. I built it out of leftover wood and scraps. I wouldn't leave anything in there all day, but its good for an hour or two, if you are around to watch it. Very secure and protected for babies.