Abstract: A roof structure for a building having end walls and side walls, the structure providing reduced air conditioning loads for the building, the roof having spaced apart purlins, roof sheeting affixed to the top edge of the purlins, ceiling sheathing affixed to the bottom edge of the purlins providing plenum areas between adjacent purlins and between the roof and ceiling sheathing, vents at one end wall providing means for entrance of outside air into one end of the plenum areas, and fan means connected with the plenum areas to draw air through the plenum areas and discharge it exteriorly of the building, thereby cooling the plenum areas and reducing the effective heat load of the building ceiling.