For a large shop of that size, a forced air, fuel oil heater would work. If you are worried about fumes, find one with a heat exchanger unit that will vent outside. With roll up doors, you need a heat supply that will replace the loss quickly when you move a car in/out of the bay.
If that is your shop pictured above, you might want to look into something similar to these:
Oil Fired Unit Heaters - Portable Oil Fired Heater, Modine Oil Unit Heater, Modine Heaters (the 3 bottom units shown) or a similar unit if you have access to natural gas. They might seem expensive but the heat sure is nice.....