Gerbils have simple needs. Most hamster cages will work well for them. You just need to make sure that you get a generously proportioned cage. While gerbils are prodigious chewers like other rodents, they don’t tend to chew up their cages. Plastic cages can easily work for this reason. Most pet stores sell modular gerbil cages. You can buy a single cage and then extend it over time by adding more units. You can toss in a few broad pipes made of plastic, too.