Due to some engineering problems, the roof does not roll off very easily.  This is due to a combination of elements.  The roof is heavy.  Also, the cannonball track I chose to use is really meant to be hung, rather than placed atop a wall.  Consequently, the roof actually rolls on the heads of bolts used to attach the rollers.  Also, the roof is so high the only way to roll it off by hand necessitates the use of a ladder.  So, using a series of cables and pulleys, I decided to use two ratchet cranks to roll the roof back.  The close crank, shown here, is mounted opposite the open crank.  This allows one person to effortlessly open and close the roof.  They also double as security.  Tension can be applied to both at once to hold the roof in one position.