if my dream self room represents my inner psyche not only would it be bigger on the inside (like in Doctor Who) but it'd be a burning hell hole with fire, spikes and clowns everywhere

I mean it could happen. It’d seem as far as we’ve seen, the sizes are still realistic to the size of the room itself in Prospit/Derse, but. John had the clown scribbling and the Jack Noir doll Gamzee made him have a nightmare about. Dave’s room was pretty much a replica of his room with SBaHJ scribbling on the walls. I do wonder the limits of how personalized the Dream Rooms are.