If you have the knowledge and plan to be hands-on with building your house, consider using that time to shop around for building materials for the new house. You can save thousands by being opportunistic and buying materials, supplies, and appliances when you find a great deal. If you are actively looking and have cash in hand, there will be times where you can buy things at a great discount.
When I was building my house a few years back, there was an earthquake in Chile that affected the price of OSB, plywood, and moldings. For example, A sheet of OSB sheathing went from about $8 to $16 each for several months. Fortunately, I missed it, for the most part.