Hi mikeg, I reccomend that book highly. I think widening the building to 14' for the dually is a good idea, but it puts more stress on the floor joists. Jack suggests in the book that if you are going to store a larger tractor or car you should bump the floor joists from 4"x6" to 5"x6". Perhaps you could support the joists mid span for the truck. Or you could delete the floor system and put it on a floating slab.
Dave
