I just had another thought. Draw up a contract between you and he guaranteeing him the job at an agreed upon price. Once the material is on site, I would include a start (window) IE: 1-2 weeks? and estimated finish time. His 5% upfront fee is likely there to keep you from changing your mind and him getting stuck with the materials which is to a degree understandable.
With the above contract notarized etc. YOU then buy the materials at his cost and have them delivered directly to your property. He still get's his profit/ markup and you at least have the materials if somethings happens to him.
That looks like a good plan, after you check his references. Also, I really bet there are building codes your new building will have to meet.
this late in the year, A pole barn will probably be the fastest build, and may be the only thing that can get put up before the ground freezes too hard, and that is really debatable at this point. I don't see how anything can even get started before Nov1st. I would price out a metal building if there is a resource in your area. The metal buildings used to be better quality (and slightly more money), but that was several years ago.
Honestly, I'm surprised you can get any 30 x 40 with 14' sidewall building with materials and be erected for the quoted price.
