The Yaheetech 40" playpen works well if you want something you can move around and store easily.

I like the Pro Select Steel Modular Cage (with modifications) if you want something more permanent. I use it for when we have to go out and it's their full time potty area. The floor grate cannot be used with IG's, their feet will fall through and they'll get hurt, you'll need to leave those out. I also leave the left side off and attach a 24" crate for the sleeping area. You can just remove the side door to allow them to get to both the potty and bed areas. As a plus, the divider that the Pro Select comes with fits to close off the bed crate when needed as well. I've had this setup for about 6 years now and it works great.