Is it possible to ad a dormer to an existing roof object? I have a hip roof that would need a smaller shed roof dormer on one face. Is that a possibility?
What you can do is to subtract a boundary from the hip roof, (with the _vaRoofSubtract command)
and then create the walls and the shed roof for the dormer. You can extend the walls to the shed roof of this dormer to get them attached.
If you need to extend the shed roof to the hip roof face, you can use the shed roof control points. And if you need to cut off the bottom parts of the dormer walls, in order they match with the hip roof face, you can use the vaWallSubtracSolid command. (you will need to create an auxiliary solid object to subtract from these walls).