Insert Room Boxes
You do not have to use the House Wizard to generate your rooms, nor do you have to reuse the Wizard if you forgot a room. The Insert Room Box tools e.g. Insert Bedroom will allow you to add room boxes to your layout at any time.
Simply select an Insert Room Box tool then click at each location that you want to place that room type. The tool will remain active until you press ESC or choose a different tool.