Whether you build a room with a cube, or make separate walls, floor, ceiling is totally up to you and what you're aiming for. I've done it both ways. The traditional 3D way of doing rooms is to turn off sunlight and use lights only. But that doesn't mean you have to do it that way. I've done rooms that were lit only by the sun. They have a different look and that's fine too. Purists would disagree of course! LOL