I haven't done much of this myself, so perhaps others can add more.
The basic stuff can be modeled with the standard tools; slabs, walls, columns, etc. Fancier bits can be made by modeling, assembling, modifying (w/SEOs, etc) and then saving as library parts. Some really detailed, custom, or complex bits may require GDL scripting. MaxonForm and the CadImage and Cigraph tools could also help.
PS. It looks like I'll be lecturing on GDL (and perhaps other stuff) in Croatia this May. Get in touch with Marin if you are interested.