I have trusses every 12 feet and rafters between every 2 feet. I do this as a hobby, so occasional use is when it will be used. So between the trusses I have clearance at the center of 12 and a half feet. I have plenty of room to work on trucks, including my 2 ton. As I get older, it gets harder to crawl around under a vehicle, even with a creeper. I think I'm leaning toward an outside lift, covered with a carport, and tarped when not in use. I am getting an i-beam from work they want to toss and I already have a trolley and chain hoist because I had an I-beam at my last house.
Thanks for everybody's input.
