++ "...and none of them are changing."
This. It seems that it is the rare project that doesn't have changing requirements of some form.
When I was in college, lo these many years ago, I did house construction for a while. It was not uncommon to hear "Can you (move|add|remove) this (door|window|wall|other)?" in the course of things. As it's a lot easier to (move|add|remove) things before you've run the electrical, plumbing, mechanical, or closed up the walls than it is after-- getting the feedback a.s.a.p. is essential to minimizing cost/schedule.
Actually, now that I think of it, not everything WAS on the blueprints as the assumption seemed to be that the contractor would figure out the missing details as they went along.