They need a wire cage, not an aquarium, as tanks end up being too small, can trap odors and be toxic, and are really more of a hassle in the long run.
Rat Aquarium Setup vs Cages
Rats need a minimum of 2 – 2.5 cubic feet per rat (more for males) and you can figure out if your cage is large enough by using a rat cage calculator (make sure you specify inches or centimeters)
Here are some cages that many rat owners use:
Martin’s Cages Inc.
Petco Rat Manor
Pet World Direct
Savic Freddy 2
ALSO SEE: Rat aggression towards other rats
Note that Ferret Nation cages have wide bar spacing, allowing baby rats or even small females to escape from them. Many people end up using wire mesh/cloth to modify these cages until their rats are large enough not to slip through the cage bars.
There are rumors of a Critter Nation with smaller bar spacing to come out in the future. Generally anything with bar spacing of 1/2″ or smaller is ideal for rats.
On top of a cage that is large enough for your rats, they also need approximately one hour or more each day of free range time. Some people dedicate an entire room to their rats where it is okay for them to roam around and explore (make sure there are no holes in the wall to get lost in, and no furniture that you don’t want to be chewed)!
If space is limited, a secure bathroom or bathtub is an option. Make sure that you have plenty of toys and interesting things to crawl in and explore to keep your rat’s mentally stimulated.
A free ranged rat is a happier rat. If you keep them locked up in their cage all day they will become restless, and sometimes difficult to handle.