Whatever you do, make sure each gable end stud is cut to length properly. The length difference between adjacent studs should be the same from top to bottom. If not the roof will bow. Make sure that last rafter is somewhat straight. Sounds stupid, but it happens all the top....trust me. Try to get away from recessed lighting in the ceiling of that cathedral room. Looking for trouble. Leave that space for insulation and baffles to carry the air out that ridge vent. Nothing worse than watching your lighting drip in the winter.