As the client, you need to remember that the builder can only work with the information that you provide them. Realise that the builder ‘does not know what he does not know’ and assumptions are one of the biggest causes of disagreement. It is your responsibility to convey as much information as you can to them about your needs and desires.
You will achieve the best outcome if you do not hold back and are fully transparent with your builder. I know that some information may be sensitive, but if you want the best outcome, you need to find a builder whom you can trust with that information.
Information that would be valuable to the builder might be: