All rats should have a free range area. Even if your rats have a large cage it is important for them to have time outside the cage to run around and socialize with you. This page provides some ideas of what to put in your play area, where to set up.
Container House - The Skyline was built by Free Range Tiny Homes in Eatonton, GA and won Best of Show at the 2016 Florida Tiny House Festival! - Who Else Wants Simple Step-By-Step Plans To Design And Build A Container Home From Scratch?