One thing I might suggest (meaning I wish I had been wise enough to do it myself), I would make the 10% plumbing and mechanical payment contingent on final approval of the city and their signoff on the building permit. Little did I know my PB never took care of that and two years later the city showed up on my doorstep and I had to deal with all the final inspections and making sure everything was up to code at that time. Just a thought, not sure if they already do that, or if it is even possible.