Many, many years ago (1983 to 1987 ish) I kept pet rats, along with my budgie, gerbils and a hamster. My first rat was a single girl called Missy, when I didn't know that you shouldn't keep them alone, and then I had a trio of boys called Tom, Dick and Harry. They had a home that I built myself, consisting of a wooden top on a 3 foot aquarium, with a wheel that my husband helped to make from a circle of plywood, some dowelling and a ball bearing.
The rats were really good and friendly pets, but I gradually gave up most of my pets as I had enough to do once we started a family. The children have kept hamsters and gerbils since then, but neither of these really measure up to rats as an interactive pet, although Pippa the shoulder gerbil (pictured right) came close once she got older and calmer.