In my opinion the builder was supposed to follow the plans and that was part of the contract. He failed to do so. You have lost out as a result. The quantification of your quantification is arguably the cost of putting it right. However, at the very least your claim would be for the value of the house with four double bedrooms as opposed to 3.5 bedrooms. A valuation surveyor can give you that information. I hope that helps. Please leave a positive rating so that I am credited for my time.
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