Lowering Roofs and Taller Chimneys

Oh! Another idea. You can build the garage with tall half-walls, then put a hipped roof over it, one square smaller on all sides. Then extend the eaves of the roof so that it covers the garage. You'd have to remove the ceiling if there is one, so that it doesn't cut through the roof. Then adjust the slope of the roof so that the edge of the eaves touches down on the top of the half-wall.