Think of it this way every sheet of plywood, 2x4 or lots of other stuff
comes in 8' lengths, try manoeuvring that around when you installed a
ceiling that is just shy of 8' when you add ceiling material etc. I wouldn't
even consider 8' and 10' is the minimum. Now in I do know of a shop that had
the roof trusses changed so that the section where the car pulls in is over
12' and the rest is 8' WORKS GREAT. Also in my area of Ontario I would put a
few rows of block down first to help keep blowing snow and rain out.