The bottom line seems reasonable given the scope of work. However, your illustration shows 2nd floor windows on the side of the garage and I am not sure I saw those windows in the quote, nor did I see any provision for trim work around the doors.
I would have problems with the payment schedule, inasmuch as you have to pay 1/2 the cost before any work is done. You might want to suggest an alternative payment schedule to protect yourself in the event of problems. One possibility would be to pay a certain amount upon execution of the contract, another amount upon completion of the footings, then framing, then siding and finally roofing.
I don't see any provision for any fill that you might need under the concrete floor, nor do I see whether they plan to put any steel (rebar or mesh) in the actual floor.
Further, the contract stops short of specifying that the contractor is actually supplying the labor to complete the roofing. It clearly states that they will perform the digging and framing, but it seems to be silent on who actually decks and shingles the roof. I would recommend that you modify or amend the contract to clearly stipulate that the contractor supplies the labor for roofing the structure within the scope of the contract.
Finally, you will want to make allowances for utilities (if any) that may need to go through the foundation in case you want to install a bathroom later.
Hope this helps, and good luck with your project.
