if your dormer is flush to the eave wall panels, then they simply extend the wall panels up into the gable of your dormer. Then the dormer cheeks and roof panels extend back and over the roof panels. Alternatively for "dog house" dormers that sit on a pair of rafters I have heard they can be preassembled, and flown over and down over the precut hole in the panel roof. Seems to me an enterprising panel manufacturer could market premade dog house dormers out of panel scraps if they put their minds to it!
