Perfect One, That's the only think I know about online that answers your question. But basically, to make windows and doors you can use the dynamic extrusion tool in the Vertex Modeler. You can select a polygon and use the dynamic extrusion tool to create a new polygon in the middle of the first one. Then you can use the tool again to extrude the new polygon into a cavity. That's the best explanation I can give in words. I hope you can find a way to register at 3DXtract, because it's a very helpful resource.