Plumbing: plumber. Electrics: electrician.

Most other things (besides obvious big things like foundation, drainage, roofing, load supporting areas) can be done with a good "fix it all" kinda person, or (with patience) youtube.

Plumbing isn't all that complicated, really. There are things you have to understand, but a little research will take you a long way.

I only call the plumber when I don't have the equipment I'd need, like cameras and snakes.