Does the money spent on construction enter into the estate of the deceased mother, and is the son's enjoyment of the building's income during her lifetime considered a right for the heirs, knowing that the mother allowed him to do so?

The fatwa we follow is that a building constructed by a son on his father's land with his permission is considered a loan ( 'ariyya ) that terminates upon the father's death. The son is entitled to the value of the building as scrap when the father dies. The heirs are not entitled to claim compensation for the son's benefit from the building's proceeds during his father's lifetime.