All excellent advice here. I would add one thing: photograph everything, every phase of construction, every excavation, the septic and sewer lines, every wall, floor and ceiling, insulation, roof panels, even the people working on the job. If it's a slab on grade, shoot the pipes with reference locations before it's buried. Photograph every wall as the rough plumbing goes in; all walls and ceilings where electrical wires, junction boxes, switches and outlets are or should be. Wherever you can, use a tape measure in the photos for spacial reference. You can't imagine how valuable this can be down the road if you have problems or want to make changes in the future.
I built our own home with help of a good framer and his son. I contracted the concrete work, the septic, electrical, plumbing, insulation, drywall and cabinets, but we did everything else including windows and doors. I installed the phone, security and sound system wires, the evaporative coolers and ductwork, did additional insulation and all the paint work. I also installed the 850 ft. utility trench for power, natural gas, water, phone, irrigation lines and remote electric power for the irrigation pumps. We did it all on 20 acres of farmland for $119K, total. The house was featured in a building magazine for it's innovative design. The house is unique, simple and efficient. It's light and bright with lots of large windows, and we love living there.
I photographed our home building project with 35mm film, before digital cameras. We put together two albums of printed photos of the construction project, all the walls, sewer, people, everything. I subsequently digitized all the images. It's the best family album we have, and the most useful. Take lots of photos, you can't take too many.