Is it forbidden for a father to build a house for his son, but not for his daughter, due to the son's need for housing and the daughter's lack of need, regardless of whether the father is able to or not?

The fundamental principle is the obligation to be just among children in giving gifts, so that a daughter is given the same as a male, or half of it. However, favoritism is permissible if there is a need, such as if a child is poor or ill. If he is capable of building a house or renting accommodation, then favoring him is not permissible, and the father must give his sister the same as he gave him, or half of it, or reclaim the house. But if he is in need of marriage and has no means to build a house, then there is no harm in singling him out for a gift.