I am installing a flat roof over my existing deck that will have a 3" slope in 15 feet. I intend to use 6X6 rough cedar posts positioned approximately 4 feet on center to support the roof. The roof structure will consist of 2X8 Douglas Fir rafters on 12" centers with 23/32" tongue & grove plywood decking. The roofing material will be either fully adhered PVC (IB Roofing Sysyem) or seamless EDPM rubber. I had planned to use 6X12" rough cedar headers over the 6X6" posts but don't know how they will need to be attached to the posts to meeet code? I could also just build the headers out of fir lumber and enclose it with Smart Board but need to know what size I need to use and how to connect the posts? Can I get advice from someone who knows the ICC Building Codes or at least a suggestion of how to proceed?