I come from a CAD background and currently work for architects. To model a
building I use Arris CAD (designed for architects) or AutoCAD with
AutoArchitect. Both packages give me walls, doors and windows which are
drawn (and inserted) in plan and extruded in 3 dimensions for a model. Thus
an architectural floor plan is used to generate a 3D model. This eliminates
many steps in going from a floor plan to a 3D model. These packages are
less than ideal for dealing with organic objects.
Once the model is made, I dxf it out and convert the dxf file to vrml with
conversion software.