darkstad,
Check out this post to see some ways of approaching this challenge:
http://archicad-talk.graphisoft.com/viewtopic.php?p=187051&highlight=#187051
In the method I described, I am applying a 2D skin to a wall. And with a PNG I can assign an alpha channel so that you can see through the skin where you want it to be blank. This method is good since it can keep your file from having too many polygons which can slow the processing of a file down. Since only a skin is applied, your file size only grows by however large the image file is and your geometry remains simple.
Andro55 describes a method using complex profiles and Solid Element Operations. This is good because then all elements of you faced will be 3D or extruded as you desire.
