You're right that robots aren't going to be able to replace plumbers or electricians in traditional building projects.

But why can't we change how new buildings are built so the method better suits robots. I'm sure with current technology we could design a building that could be built entirely by robots.

I don't think it'll happen because it will take a lot of time and money to develop such a holistic system, with no return on profit until it's a complete system.