first and second rails supported by the substantially top upper surfaces of respective ones of the ceiling joists, said rails being oriented substantially perpendicular to their respective underlying ceiling joists, each of said rails is of a generally U-shaped cross-section defined by a base having first and second opposite side edges, said base including first and second side walls depending from respective ones of said opposite side edges of said base, each of said first and second opposite side walls having an outboard edge, said outboard edges of said first and second side walls resting on the flat top surface of a respective one of the ceiling joists to define a void space between said base, said side walls and the flat top surface of a respective one of the ceiling joists, thereby positioning said rail fully above and beyond the flat top surface of the ceiling joists;

a plurality of rollers mounted at spaced apart locations along each of said first and second rails such that the respective location of each of said plurality of rollers is substantially fixed with respect to said first and second rails, said plurality of rollers being mounted within said void space at spaced apart locations along the length of each of said rails and axled between said first and second side walls of said base, each of said rollers being axled within said void space a distance of greater than about one-half the diameter of said roller whereby said roller protrudes from said void space above and beyond said base by a distance less than about one-half of the diameter of said roller; and

one or more platform dollies adapted to be positioned on said rollers of said rails for reciprocatory movement of said dolly along said rails, each platform dolly mounted on said rails is fully above and beyond the flat top surfaces of the ceiling joists.