qqh please. do you have a chance to talk to their construction gm, financial head and/or ceo if possible? in addition to email, try to talk to them on the phone or meet them in the office. but first thing first, as lots of other people already pointed out, you have to know what you want from this and what you can compromise. And think about how much that losing ~100sqft will impact your daily life if live with it. if you think that's no big deal, move in and forget it. or if that's very big impact, choose to build a new house. of course, all these are based on the builder is willing to give you a reasonable compensation that you agree on for all those frustration and inconvenience the builder brought you by their mistake.