If the elder sister, at the time of building the first floor, had clearly said to her brother that she was spending the money as a loan and would take it back later, then she can ask for the money she spent. If there was no such thing and the sister constructed the floor with her money as favour and kindness, then it is not right on her part to demand the money. If the sister, besides the two reasons, had built it just for no reason and she is not ready to hand it over without money, then the question should be written again. The younger sisters as well as other heirs will have their shares in the house left by the father.
Allah (Subhana Wa Ta’ala) knows Best
Darul Uloom Deoband