I can't speak much to the construction end of it, but things like plumbing and electrical were still contracted out because of code/liability issues. There were many "subject matter experts" checking things out.

For the drafting side, we agreed on a design and used our learned techniques to create the drawings, guided by Mr. Hansen and a residential architect. The plans had to be proofed by an engineer and the usual building code folks with the city.

The kids design and build the thing but there is some oversight to make sure everything is up to snuff. From my experience and what I've been told over the years the houses exceed code standards in many ways which is one of the reasons they always sell quickly. Word gets around fast in this area.