You're going to be buying LOTS of stuff the contractors will not be providing for you. Think appliances, flooring, lighting, shelving, etc. etc. etc. This stuff adds up quickly.
While I know it doesn't compare to the cost of building the house, all these little extras add up to quite a bit. I know that we used our old GM Card for the purchase of our new home and ended up with quite a nice discount on our next car.
Mary