I have just retired from 30 years in commercial construction and, in my experience, it was far more common for the GC to give the client a gift than it was for the client to give the GC a gift. In fact, I do not recall ever receiving a gift from a client. Maybe that is a reflection on me but I hope not.

Our GC gave us a gift. This was about 1-1/2 years ago when the local building business was down and contractors were very happy to have projects to work on.

You should receive a gift, not give one.

You could buy the crew a nice lunch and or beer at the end of the workday on the last day they work before Christmas. I do believe that would be about it in my opinion. If the GC's super had been on site constanatly and you feel he did a good job watching everyone's back (including your's) you might give him an envelope ($) if your so inclined as well.