I've got two friends with large shops, 36x36 and 36x48. Both are nominally 12 ft clear, pole barn, metal, poured concrete floor. 4 post lifts. At 5'10", I'm comfortable under the Nomad, my bird, any lower car. They're both 6"1 to 6'2". They have to watch where they stand up. One has bad knees, and he rolls around a lot on a drafting chair. OK for light work, but not much leverage for heavy work.
Put the wives DD SUV's, or the big pickups, and I can't stand under them before they hit the trusses.
The 4 post have some disadvantages, it difficult pulling a motor because the front bars won't let a cherry picker in. If you lift the car to get it under, now your working pretty high, and need a bigger hoist to clear the front structure as the engine comes out.
So it depends on you and your projects. We're getting on in age, and we lift the cars to clean the wheels, or buff the sides. No bending over if we can avoid it.
IIRC, there was a big price premium to go past 12 ft due to the cost of the metal siding. But we're in an urban area, so not a lot of call over 12 ft till you get to real commercial metal buildings.
