Very interesting Charlie. Congratulations on a painless reroofing...not always the case. Looks like typical Yankee ingenuity at work...I've never seen one of those buggies here in the midwest.
Here every building I've even owned has had a 10" sandwich of old roofs, laid one on top of the other, dating back to the 1880's. The first couple of old roofs at the bottom were tar-and-gravel, with the gravel stones still imbedded! Tear-offs take weeks, with dirt and debris flying throughout the neighborhood. And the bared roof boards have to be temporarily covered and sealed each night...and you hope any rainstorms are very light until the final roof is in place. Replacing landscaping afterward is a given.
There's been a revolution in roofing materials. I've been roofing with
membrane roofing material, that is actually set afire as it is assembled in order to weld the entire roof together into a seamless sheet. It is not uncommon for a careless roofer to set the building on fire during this process. All and all, weeks of trauma, even if no roofer falls off a ladder.
So I envy the speed and expertise you enjoyed...hope the roof is trouble-free for many years.