I do not think you can import and create from your 2D auto cad drawings because the walls, doors windows, roofs etc are all different entities (they are of different thickness, color, height, material etc) . Yes, Revit is one of the top of the range programs for Architectural design ( you can only import 2D files from Auto CAD and add details to your Revit 2D drawings). You can create curved elliptical tube trusses etc, I saw an example tutorial on one of these sites, http://www.rugi.org/download.htm , http://www.revitcity.com/ , http://www.karelcad.com.au/default.htm , check them out. It would certainly make life a little easier if we could import/export 3D files from/to the Inventor, or maybe combining the two software's.