Guinea pig cage with combitech®-connect. Would be good for rats too.
Idea for ferret "DIY Chinchilla Pet Cage; outside view of a chinchilla cage we fashioned from a secondhand armoire.
The Bunny Palace (indoor rabbit cage) - IKEA Hackers for pet DIY
This tutorial will explain how to make no-sew fleece liners for your rat or other small animal cage. I have a Double Critter Nation from Midwest, so those are the dimensions included here, .