back in 1990, I bought an adjacent piece of property with a pole barn that had been moved to the site. The previous owner was a real scrounger who found someone tearing down a barn, and moved it to his property. He paid little for it, but I remember him saying he really didn't save much over the cost of building new.
Some of the metal was damaged in the process and had to be replaced. He also had to rent the equipment necessary to dismantle and re-erect it, as well as pay a couple of laborers to help.
I've since had to do work on parts of the building to correct a few areas that weren't assembled properly.
Unless you have the equipment and labor on site for a project like this, I would seriously compare these costs to that of building new.
I'm planning to add a building in the near future and wouldn't consider buying & moving one. Around here, there are several Amish owned companies that erect pole barns at a price I couldn't match by buying used.