Dormer extending through roof, can't cut

[pete3m]

This is a model I received from another architect and I can't get one model component to work - in this case cutting a dormer at an angle so it does not protrude through the roof. What's the best way around this? I don't have an option to create a void or to cut the geometry with the roof. Any help appreciated.

[ToanDN]

If the join roof tool doesn't work, then create an in place void extrusion to cut it.