Here we ago again. Don’t let’s waste our money on professional fees, let’s listen to the builder and when things go wrong, expect sympathy.
If a working toilet, raising floors, damp proofing isn.t quite major, unless you know what your doing, what is.
I assume you will reply on the builder for the floor spec., type of dpc and remedial works after, to specify and just believe what he says and pay for what he asks?
Read the numerous sob stories and perhaps you will take professional advice then.
My response may not be appreciated, but at least it make make the person asking the question think just a little?
Finally “Most builders obtain the licences anyway from what I hear” if you rely on what you hear and not what you know. SEEK PROFESSIONAL ADVICE.