Earlier quoted context omitted.
Building one structure is a series of low skill tasks. Building many structures (or any given sub-specialty, e.g. plumbing) on a predetermined schedule and budget and making money doing it without charging so much money that you get undercut out of business is what requires skill. For N=1 you rarely have to be a pro to do it right.
You speak pretty definitively on the topic. I'm guessing you have some experience with construction that's worth sharing? Would love to hear a positive story of how it turned out!
I spent a few years doing under the table construction and also picked up the skills to work on mechanical things around the same time. Then I went to college, got a career and spent some money picking up the skills required to work in metal. Electrical and plumbing (not just for water) are things you kind of have to pick up along the way. I'm no means a professional at any of these skills because I don't get 40hr of practice a week. Nor am I unique. A lot of successful people from blue collar backgrounds wind up with similar skills. Even though I have software money now I couldn't afford to pay people to build the things I can build myself.