We owner built a geodesic dome with very talented subs (we would definitely not have been done now if we hadn't) As it was we were over 2 years in construction. We are not fully eco, but we did employ as much green tech as possible. We have blown in soy-based insulation that is fantastic, partial rock floor to soak up the heat, (bamboo & cork in other areas). The house is sited to maximize passive solar. We did energy star appliances and mechanical systems, variable speed pump, low flow toilets & showers, low voltage lighting, radiant heat powered by an outdoor wood boiler, low e argon windows, and many skylights to avoid the need for ac.
It has been an adventure to say the least and I highly recommend reading up on building or general contracting your own home - it is a very involved process. Almost all of our environmentally friendlier options came at a substantially higher price.
We'll be broke for quite some time, but I absolutely love waking up in my dream everyday.
eta - solar and wind are in our future, but we just don't have the $ right now - we did go through the planning/building phase with that as the end goal.
This is the company we worked withhttp://www.naturalspacesdomes.com/