I work in a somewhat better insulated building in Alabama without air conditioning. I have a small unit but don't use it. Instead, I have a big-ass fan that blows up a torrent which I place next to the roll-up door. That gets me through all but the hottest of days.It's basically impossible to work in a raw metal shed in Florida in the summer, so, air conditioning, especially when you get a discarded one for free while installing central air conditioning.
I am often welding (I'm a frustrated metal worker) and so I need the shop to be open most of the time. The only problem with that is keeping mosquitos out.