do guinea pigs need enclosures?

I've never owned a guinea pig, however i do want to one day. I have 2 rabbits that live in their own room, i was planning on giving the guinea pigs their own room too, just cuz its a lot of space. i see many posts here that use ac grids and they just run around in there. is that necessary? i'm able to modify the room with platforms, and stuff etc but are the pigs not suitable for a whole room?