not sure what kind of well you have but mine needs repairs to the pump (twice in 20+ years) sometimes and i think a greenhouse over it would be in the way.

Randy is right with the need for repairs. They have to pull the pump or points on a shallow well they need complete 360 degree availability. In a greenhouse the whole frame would to be moved about ten feet around the well. I would believe the easiest was to go would be to simply dig down to outlet of well and connect a new line to the greenhouse and possibly to each greenhouse at that time
James