Keeping an eye on things is the way to go, I seen too many mess-ups that go unnoticed or covered up until too late. Something as simple as using the wrong cement, or too little water or too much water and the pillar or wall just crumbles over the years, or the electric outlet just pulls right of the wall, or switches are in the wrong place, all sorts of things can go wrong. Some contractors cant read the house plans and they are making it up as they go along. Remember also that lowest bid does not necessarily means lower cost.