I have recently been using sh3d and am slightly good at it, however......i am finding it extremely difficult to create a roof and a floor for a 2 story house.
Floors and ceilings are defined by the rooms (doubleclick the room icon within the wall.)
For roofs:
- Either use one of the roofs from the download page.
- Or draw a wall the size of your roof, export it as .obj file, and re-import turning it to the correct angle.