بسم الله الرحمن الرحيم
(Fatwa: 1093/1093/M=9/1434)
In the case mentioned above, you may take the same amount from the builder which you have given to him. The additional amount is interest and it is unlawful to demand the same, though the value decreased.
Allah knows Best!
Darul Ifta,
Darul Uloom Deoband
