That's what I'm going to do next summer...install a big natural gas heater. I built a 18x30 shop building after we moved in last year. Then I had a chance to get it insulated last winter...spray foam baby!!! Now my shop is an Igloo cooler!
An electrician friend had an extra 220V electric heater, 18,000-20,000btu I think, so I hung that. Does well down to about 40* outside, keeps me around mid to upper 60s. When it's in 30s or below I fire up one of those propane patio heaters! I can work in a T shirt...lol. I crack the roll up door open about 6" for fresh air...and the neighbor kitties like to come in and warm up .
A regular NG heater with a thermostat would be much better! One with A/C would be even better than that !!!