A roof vehicle has a chassis, a plurality of motor-driven wheels coupled to the chassis, a man-basket coupled to the chassis, wherein the man-basket is moveable on a y-axis and is configured to lower to an elevation beneath that of the plurality of motor-driven wheels, a deck for transporting equipment, and a power supply. A method for assembling and installing a roof involves moving the roof vehicle to the desired location on the roof of a structure, lowering the man-basket at least partially beneath the surface roof, and performing work (e.g., welding) to secure the roof to the structure of the building.