if it's a big reputable building firm they will have everything done for you in the price. No need to get any plans signed off ,build what you want on your own land.
From personal experience building my house years ago, a reputable builder will ask you for payment in 4 stages the last payment on completion, when you are happy with the finished house.
Give time for any faults before last payment, ie cracks ,plumbing, drainage, etc.and yes if your wife or family don't know the builder be on site during the build
not getting into a debate mate only saying someone posted it had been suspended due to technical issues, I went through in June it was the old imagration system. It was up and running with no problem yesterday, only saying.