The roll-off roof is carried by six ball bearing dolly wheels mounted on the underside of the roof plates. They run in tracks made from halves of 2x2" aluminum square tubing, sandwiched by ¾" wood strips mounted on 2x4" wall plates. The roof rolls off smoothly onto the 'porch' area which is a similar enclosure now used for an imaging setup. It is an either-or situation, only one can be used at a time.