This may only apply to custom build and tenders. I am keen to know once a tender is negotiated, how do you ensure that the builder is using the material as per negotiated and not a cheaper version? Obviously certain things you can just look at the brand (ie: appliances) but other things such as material, the range of windows and doors etc are harder to know (ie: a sliding door from commercial range of a certain brand vs a sliding door from their residential range). Is it normal to ask for quotes / invoices from the builder as proof that they are using what has been negotiated? I have done this with one of my builders and they seem to not take it very well and say that this is their confidential information.