For your convenience, @gester, I have attached some screenshots showing the type of modeling that you are looking for. These tools are part of Blender’s Archipack, created by Stephen Leger, who has done some amazing work, and allows for parametric architectural modeling, where walls know they have layers, windows know they have hosts, and so on.
The scene below was modeled in … well, perhaps a minute. And yes, the diagonal cladding is parametric, and creates holes for openings. The stair is, of course, also parametric. The floor boards, also, are parametric. The little kitchen cabinet is a drag-and-drop library part.
As you can see, it is very easy to plug these “parametric” shapes, as well as any custom modeled shape (or pretty much anything - generated, using visual programming like Sverchok, the Blender equivalent of Grasshopper, or anything you can imagine) into IFC data, and export into IFC. At the end of the day, it is just geometry.
See this test export I was playing with:
I think there is opportunity to create a tighter integration with Stephen’s work and some of the IFC stuff I am doing to make it even simpler for users in the future.