The room has to tile on a 16 x 16 x 4 grid -- its interior will probably be smaller than this (its walls and ceiling will presumably stick into the area somewhat), but a passageway leading out of it (and presumably to an adjoining room) would need to end at the edge.
The floor needs to be at zero level at the edges for similar reasons.
The floor needs to be at zero level at the edges for similar reasons.