Best/Most Affordable Material to use for Long Rafter
You may want to go with a TJI (truss joist) that is made by one of these companies (Weyerhaeuser, Georgia Pacific, etc.,). Unless you use a 2 lb foam in the rafter bays, you will need something 14" or taller to get enough insulation in the ceiling to meet code. Of coarse, this depends on the area you live in. Different regions have different R-value requirements.