OK I deleted the whole roof and redrew it. I then had to break it into pieces, slice and dice, to get the shape back. Then exploded it and drew a poly line on the lower surface and converted it to a roof slab and tried again to change that upper angle to plumb by going to edit tool, selecting the slab and then holding the shift key down and clicking on that edge and... wait for it... nothing happens... I can't make this work on the drawing I am working on. If I go back to the sample drawing that I attached earlier I can get it to work fine but in this drawing, nothing. I have restarted program and computer numerous times... still the same result. The roof miter tool has never worked for me. It does absolute nothing. Cussing out loud at my screen doesn't seem to do anything either.