For Johnston, it's impossible to put a price tag on the thrill of creating something she really loves and that is also valued by the Guckenheimers. "This family sees the importance of treading lightly on the earth," she says. "They were so happy with the house concept that they didn't need to change much. In exchange, they got an easy, low-stress design process out of everything — and a home that reflects their life philosophy."Related article: What's Up With Prefab?