1) Add a 1st floor, adjust is height so it would look like a foundation;
2) Apply textures, if needed;
3) Add a 2nd floor from floor adding menu;
3) Drag a certain room form from the catalog on it;
4) Proceed with other actions, like adding doors, windows, furniture, etc.
P. S. Since entry door is now a little bit more up, use stairs from oi catalog or create Your own with Magic Cube tool.