Before construction can start you must get through the design and permitting phase. Ideally you will want to involve your builder during design, so you can get real time rough budgetary guidance during design. Some contractors are design-build, meaning they will handle the design and construction of your home.
Design consists of several sub categories:
Site, and septic design
Architectural Plans
Structural Engineering
Interior Design
Other Preconstruction activities include:
Permitting. building, septic, and larger lots will require a Land Disturbance Permit too.
Budgeting. Selections and allowance are defined. The more detail the better here, spend as much time as you can up front to define every selection possible, this will make your budget accurate as possible.