www.farmhouserats.com/Housing-+-Cages.php

"Wire cages are standard when it comes to housing rats. Rats should not be housed in aquariums or plastic tubs (with the exception of mothers with very young babies.) These types of housing do not provide the rat with adequate ventilation, enough space, or any surfaces to climb on. Lack of ventilation can cause temperatures to rise dangerously, as well as allow for a build up of ammonia inside. Lack of space and climbing room can cause both health and tempermental problems. Rats need a cage large enough to get exercise in, even if they are taken out of the cage regularly."