The present invention is a curb assembly system for modifying a metal building. The apparatus comprises a plurality of mounting brackets, at least two caps, at least two side rails, at least two end panels, and a plurality of screws. The mounting brackets are placed on support structure of the building, one of the at least two end panels is placed at the low point of the building, one of the at least two side rails is placed on the edge of an existing building panel, the at least two caps are placed a determined distance from each other, another of the at least two side rails is placed parallel to the first side rail, and another of the at least two end panels is placed at the high point of the building, such that there is created a “curb” comprised of the side rails and caps which can support an device or feature that is secured thereon.