Nobody asks about sound before they order and almost everybody mentions it afterwards. Three of the four problems are solved on the drawing.
Rain on a metal roof is the classic complaint
A standing-seam roof directly over an insulated deck drums. The fix is mass and decoupling: a heavier deck board, a resilient layer under the seam and a fully filled cavity. Done at production it costs little; done afterwards it means stripping the roof.
If the house is a holiday let, weight this heavily. A guest who cannot sleep through rain writes the review that sets next season's price.
Footsteps on the loft carry straight down
A lightweight loft deck transmits impact sound into the living space beneath it — the one place where somebody else is sitting. A resilient layer under the finish floor and a filled void between the joists cuts most of it.
This is the cheapest acoustic upgrade in the house and the one most often left out because it is invisible on a specification.
An internal partition has to have mass
A stud wall with a board each side and nothing between separates the view and nothing else. Filling the cavity and using two layers on one side takes a partition from useless to genuinely private, and costs a few centimetres of plan.
If the point of the room is that someone can take a call in it, say so before production. The wall gets built once.
Appliances are the background you live in
In an open plan the extractor hood, the ventilation unit, the fridge and the dishwasher run in the same room as the sofa. Specify each by its rated noise, not by its brand: below 50 dB for the hood, below 45 dB for the dishwasher, and a ventilation unit whose spec sheet gives sound power, not just airflow.
Site the MVHR unit away from the sleeping area and on resilient mounts. It runs continuously, which is exactly why it must be inaudible.
Soft surfaces do the rest
A compact interior with hard floors, glass and plaster is reverberant, and reverberation is what makes a small room feel busy. A rug, curtains and an upholstered seat drop the reverberation time enough to be obvious.
This is the one acoustic fix you can make after handover, and it is worth doing before concluding that the building is at fault.