To create rooms with multiple levels, you will need to use a series of Cubic Boxes.
Ceiling
1. Change the ceiling height to the full height of the room.
2. Use a cubic box to fill in the area of ceiling. The height off ground will be the distance between the floor and the lowered ceiling. The height will be the remaining distance between the height off ground and the overall ceiling height.
Floor
1. Change the ceiling height to the full height of the room. (This includes the height of the raised floor level).
2. Use a cubic box to fill in the area of the floor. Alter the dimensions but leave the height off ground as 0. The height of this cubic box is the height of the raised flooring.