I want to draw a room inside a room.

A 16' foot tall wall at back.

An 8' square "box" against the back wall.

Stairs on either side of the box that lead to a floor that people can stand on.

A railing up the stairs that cross the box....

A door into the box below. (The box is a room within the room.)

I can draw the walls, but I can't put a ceiling inside the box that will be a floor on top of the box. Is that possible with Home Sweet Home 3D?