Is the aforementioned distribution of the house, in which the cost of building an entire floor by one of the sons was not taken into account, fair from a Sharia perspective?

The floor built with your own money is considered your private property unless it was a gift to your father. Your father does not have the right to dispose of it except with your permission. Your father's acceptance of your building above his house is considered a gift from him of the air rights of his house to you. As for your father dividing his money during his lifetime, it is valid if it is a fair gift and transfer of ownership, such that each person disposes of what was gifted to them. Otherwise, it is not valid if the execution of the ownership depends on his death.