I have drawn a dutch gable roof inside a parapet with a corner cut off as it is on a street corner/ intersection.
I used roof tools( gable) and then edited manually.
I chopped out unwanted roof so it is all inside parapet and healed lines and used sandbox to heal surface which filled with roof again.
We want to help you the best we can, Could you please attach a few screen captures of your model in regards to what you are talking about and I will be able to answer your question in detail.