I would build it wider than 14' wide.
Are you and the contractor talking the same 14' wide? He's probably talking outside dimensions and your probably talking inside? If outside dimensions, by the time you have 2x6 studs, that only leaves 13' inside by the time you put on the inside sheathing.
Your rig is probably 8' 6" wide, subtracting that from 13' leaves you 4' 6" or 2' 3" on both sides of the rig. How far do your slides come out? I don't think you'll have enough room to walk outside down the length of your rig, you may have to go outside the building to get from one end to the other?
Go at least two feet wider - that only adds one foot on each side. And a 13' tall door is asking for trouble. Go with a 16' ceiling and a 14' tall door. Even at 16' tall, how are you going to get on top of it if you want to do any work on the roof while inside?
You may fit in the dimensions you're thinking about, but are they really going to be usable?
Bill
