I was so happy with this cage that I immediate purchased the add-on expansion to replace the cages for my other critters.  The add-on allows you to divide the cage into two separate levels, and some creative use of corrugated plastic allowed me to divide the top level into two smaller town-houses for my hedgehog and rat that prefers the company of people to other rats. I may even get a second expansion soon. The perfect solution to combine all your small pets into one footprint.