What do you call someone who....

[Nelly111s]

most builders are ex prisoners and criminals, just something to bear in mind, I've had some very bad experiences with builders, there's very little trust or faith I have in them.

That’s one of the most, if not the most, fact-free post I’ve ever read on here.

 

[TRITON]

Tarring every builder with the same brush because of your bad experiences really isn't necessary is it?

Although it should be noted that only 1 in 3 pigs is a competent builder.

 

[Jake]

Which maybe is why things tended to work better decades ago when many surveyors, Q.S.s, engineers, architects etc. had worked their way through trades and "night schools" on the way up.

Possibly. I think the loss really is in the craft tradition. In large part, things have moved on and the starting point is higher education than it used to be. I don't really believe that things tended to work better decades ago.

 

[XH558]

You could also consider a building surveyor.
They are very good at adaptations, extensions etc.