Guinea pigs are social animals and can live with others of their kind in the same cage, but be sure that enough space is provided for each animal. Partitioning the cage is suggested to provide each animal with separate sleeping quarters. Male guinea pigs should not be housed with young ones. If you notice any signs of aggressiveness between guinea pigs living in the same cage, separate them at once. Some guinea pigs will engage in "barbering," or chewing on each other's hair. This is not usually an aggressive act, but rather may be due to boredom, excitement, a hereditary behavior or perhaps a dietary deficiency. If the barbering becomes stressful or harmful to one or more of the guinea pigs, however, you should provide them each with their own home.
Piggy's cage should be at least 18 inches high, 24 inches wide and three to six feet long with a solid floor (wire floors are irritating and can lead to foot or limb problems). Be sure to place the cage in an area free from drafts, chills, extreme heat and sudden temperature changes. Also, keep your new friend in a quiet area with few disturbances. The cage may or may not have a roof to it; if not, be sure that the walls are high enough to prevent escape, and that no predators (mainly other household pets) can reach into it. The lower three inches of the walls should be solid-this prevents bedding and food from being scattered outside, yet still allows the guinea pig to see what's happening around him.
The cage should be easy to take apart and clean. Make sure it's well-ventilated (no glass aquariums!), with no sharp edges or corrosion and no small openings that can trap Piggy's feet or limbs. The cage should also offer your pet a place to hide (see below for objects that you can put inside to make life more interesting for him).
You'll also need to provide at least two inches of bedding for your new friend. Shredded newspaper works well. Whatever type of bedding you use, it must be nontoxic, nonabrasive and inedible, as well as dust free and absorbent. Also, make sure no sharp objects are mixed in it. The bedding should be easy to form into nests and tunnels, as well, since guinea pigs like to nap and hide in these. Sawdust should never be used, and while cedar chips are a popular bedding choice, they do tend to make your guinea pig's coat a bit reddish in color.