Waste Less Works has recently salvaged 96  panels ranging from 14 1/2'x4' to 16'x4' for a total of 6,000 sq ft.  They were pre-built and designed for roof loads.  The construction is a stressed skin panels with plywood on each side and 2x6 solid lumber on 16" centers glued to each piece of plywood.  These are the former roof panels from the old Grimebusters Laundry facility in North Trempers mall. They are 6 5/8" thick. $50 for each of them. 

Structural Roofing Panels