A building structure has a generally horizontally disposed modular roof made-up of a plurality of side-by-side roof units which are mutually joined. Each roof unit is constructed as a pair of spaced apart rigid skins shaped in such manner as to eliminate additional supporting structure and which are joined along mutual edges of the pair of skins and forming an interior space filled with a thermal insulator. One end of each of the roof units is curved in a downward arc. A skylight frame protrudes above an upper one of the pair of skins, the frame supporting an upwardly facing window. An electrical circuit includes LED lamps mounted in a lower one of the pair of skins with its illumination directed downwardly. The circuit may also include a motorized shade or a liquid crystal shade for limiting natural light transmission through the window.