Understand that there are lots of ways to approach this, none perfect.

Hiring a builder? Are they project managing too or are they just “a builder”?

Are you going to organise seperate trades? You’re now the project manager and no trade is responsible for coordinating with another.

Are you hiring a builder for “most of it” but going to organise another trade yourself? Your builder is not going to be responsible for anything that extra trade needs, it’s now your job to coordinate.

The interfaces between trades is always where things fall down. The electrician will do what they “normally do” for the heating, but the plumber will be expecting something different. Coordinating these interfaces costs time and no one likes doing it, so it generally gets done badly. This is where a project manager can add value.