[Porsche-O-Phile]

Stairs and roofs are always a pain with any 3D modeling program (as is topo, but I won't get into that - plus you're a CE so you probably know ways to handle that...). I haven't used this one personally but if you're having difficulty possibly consider using Google SketchUp and exporting the model & importing into this program if you can. SU is the most user-friendly modeler I've come across and we use it professionally, then build our technical Revit-based models off of the SU schematic models.

Good luck.