Considering adding an addition with open "cathedral" ceiling (to avoid trusses). Span will be 20' with 2' roof overhang on each end. I'm considering 2 or 3 2X10's laced together as ridge beam (since it will be supporting the load) supported by several vertical 2X4's burried in wall to support the beam. Rafters probably 2X8's or 2X10's on a 18' span resting on beam. Is this enough or do I need a engineered wood lam for the ridge beam? I would probably do mockup beams accross acting as cross beams or ties on 4' centers. I usually overkill. Am I on track?