An apparatus used in roof construction wherein insulation material is held flush within the channels formed by the apparatus. The flush engagement between the insulation material and the walls defining the channels of the apparatus leads to a greater surface area securing the insulating material in place. The apparatus includes attachment means on its top flanges to mount rebar members to the apparatus holding the rebar grid in place. The vertically disposed flanges of the apparatus include openings that allow concrete to pass through the apparatus preventing fatigue points caused by the interruption of concrete. The apparatus can be employed in a method that allows a roof to be transported to a job site with the rebar grid already secured to an apparatus.