I made mine with a piece of 4" I-beam across the room, supported at each end by 4x6's on end from the floor. All this stabilized to prevent tipping. Floor and upper attachments by sandwich plates. Instead of a trolly on the lower part of the I-beam, I use a wheel on top, with side plates hanging down to a pin I hook a chain fall to. This does require a fair amount of height, but works great.