Don't expect your custom home builder to be a mind reader. Often a custom home builder will only work on a few homes at a time, so they have the opportunity to really get to know what you want. The more specific you can be with them, the more exactly they can match your needs with regards to your custom designed home.
If you want to make a gradual shift to solar energy, it may be worth your while to invest in solar water heaters after your conventional water-heater conks out. The payback for solar water heaters is much quicker at about five to six years.