Honestly, I would say that if this guy is not a contractor and if this is his first custom built home, he is NOT allowed to do ANY of the work himself.
If you let him do the work, neither of you will be happy. The best thing that you can offer him is to lay the cheap self-stick tile and to paint the entire house with Kilz primer. Then once everything is done, he signs off and gives you your final payment, he's free to do whatever upgrades he wants to.
But I believe that if you let him work on your jobsite, he will start strong but you'll end up finishing the work for him for free just to get him out of your way.