Other than size, mice and rats have essentially the same requirements for housing. A wire cage is best, allowing for 12 x 24 inches of floor space for 2 rats or 4-5 mice. Glass cages do not allow for good ventilation. The wire cage also encourages the animal's instinct for climbing and offers exercise and stimulation. Your design can expand horizontally or vertically, depending on the space available to accommodate ramps, wheels, climbing platforms, ladders, and other toys (toilet paper and paper towel cardboard rolls make wonderful tunnels for running). Mice and rats need and enjoy a lot of exercise, so be sure the cage and accessories can fill this need.
Mice and rats prefer to have places where they can hide and sleep undisturbed, as well. These can include cardboard tubes, PVC pipe, and small clay flower pots. Rats and mice like, and need, to chew, so wooden accessories provide for this need but often become unusable after a short time.
Bedding should be free from oils or preservatives, ruling out cedar or pine shavings. The recycled shredded papers available make a wonderful substrate and are environmentally friendly. Aspen shavings can also be used. Shredded paper towels work well for "nesting," which they like to create in one corner of their environment. Heavily soiled areas of substrate (bedding) should be removed daily, while the entire cage should be thoroughly cleaned and bedding changed once a week.
Ideal cage location is in a relatively quiet area which is still within view of what is going on in the home. Placing the cage on a table or stand will help your mice or rats feel more secure. Avoid placing the cage in direct sunlight or drafty areas and prevent access to the cage by other household pets, especially cats and dogs.