A gable dormer is framed by marking existing rafters and cutting out the area the dormer will occupy. The remaining outside rafters are doubled with same size lumber. A doubled rafter header caps the cut rafters at the bottom. The front dormer wall sets on top of this header. The two side walls set on the doubled roof rafters.
Top plates cap all three dormer walls.
Once that dormer ridge board is nailed in, each valley rafter can be cut. Some dormers may have added rakes and eaves to protect and decorate the dormers. The lookouts are capped with fly rafters that run at the same angle as the truss rafters. A soffit board can be nailed on the bottom of the lookouts to finish off the rake. Eaves are created by extending the dormer rafters past the side walls.