Guessing that you mean a lay bin. Choose the one that is the biggest that you can fit inside your enclosure. You don’t want to put anything on top as once she starts digging her tunnels, whatever you put could fall on top of her and trap or hurt her. Do make sure to put a branch for her to be able to easily get in/out of the bin. I like to have at least a couple of ways and try to have a pothos vine dangle in/over the bin. You want to fill the bin to only about 5-6” deep with washed play sand. It needs to be moist enough to hold a tunnel without collapsing when she is ready to lay. I always drill some tiny holes in the bottom so water can drain rather than it becoming a muddy mess. Usually they have a preferred poop spot. If you can find hers, try to put the bin away from it. If she does poop in it, just remove the soiled area.