OK, you've got the right cage and the right bedding. But you can't just plop Piggy into his new home and feed him now and then. The cage will need to be cleaned and the bedding changed. And guinea pigs thrive on loving attention and play, just as cats and dogs do.
To keep your pet's home clean and safe, change the bedding daily. Once a week, thoroughly wash and disinfect his cage with a solution of one ounce of bleach mixed in a liter or quart of water. Be sure the cage is rinsed well and completely dry before adding fresh bedding and putting Piggy back inside. Rinse feeders and waterers every day, too. And keep your friend's home dry, as dampness can cause illness.