Guinea-Pig Exercise

My guinea-pigs live outdoors (although they are in the shed for the winter) and normally they go in the run, but if your guinea-pigs live indoors do you have an indoor run or do you just let them run round a room (obviously away from wires and things like that)

Run around the room lol. Only it does get reuben(rabbit) a little upset when he comes back in and find cavy smells everywhere. :p Also, on my mum's double bed, and outside runs when it's fine.