Ceiling mount heater
Generally I don't like overhead heat because my feet are always cold. But it is too late for that. BEST way to heat a shop is to install redundant liquid loops into the floor when it is poured. You can heat the liquid (essentially anti-freeze) in a number of ways.........a furnace like Steve in PA showed, with heat exchanger loops in the stove/ furnace.......some type of boiler, some guys around here even use just a water heater and a circulating pump. The floor does not have to be very warm to make a big difference in the shop
So far as overhead you want it to be quite a bit OVER sized for the building compared to "if it was a house." This is obviously because the shop is never that tight nor insulated, but also because you want quick heat up so you don't have to have it "up" all the time, and also because there will be times you have to open the door........and want quick recovery.
Be sure to think over the location. There is only so much you can do in terms of directing the fan, so you don't want to be working in the coldest corner, nor do you want to be working in the direct close in heat blast.
IF THIS IS combustion, IE gas/ LP think carefully and heed the install specs. IS THE BURNER "sealed" that is "outside air for combustion?"
THIS IS IMPORTANT. Back when I worked on this stuff, I was in several buildings where A SITUATION WITH AN EXHAUST FAN caused a negative pressure situation in the building, causing the heater to "reverse" vent DOWN the vent. This puts combustion fumes INTO the building, or if the burner has "spill" safeties, it will shut down the burner.
Be sure to install it with plenty of clearance under it for tall vehicles, as well as "someplace" you can access it with a ladder for service. You don't want to have something difficult or impossible to move under it, later. As a then service man, I've dealt with this and it's no fun. I walked away from a couple of jobs because of obstructions unsafe or impossible to deal with. Also heed clearance rules I don't remember anymore........I think overhead unit heaters are supposed to have 8' clearance to floor minimum, but check things like that. You leave yourself open to trouble in case of insurance/ claims.