Is the eldest son entitled to control a larger area than his father allowed him to build upon, and what is the Islamic legal status of the amounts he spent on the expansion, and are they to be calculated from the value of the inheritance before or after its division?

The mentioned transaction could fall under one of the following cases:

1. A valid gift during the father's health and lifetime: If the father gifted his son a part of his house to build upon, and the gift was valid and permissible according to Islamic law, then the son only owns what was gifted. Anything built in excess by the son is considered usurpation (ghasb), and the heirs have the right to demolish it or take its value as debris. What was spent in the case of usurpation goes to waste.

2. A gift during the father's death illness: This gift takes the ruling of a bequest (wasiyya) and is not valid for an heir unless the rest of the heirs approve it; otherwise, it is void. In this case, the son is treated as a usurper regarding what he spent.

3. Permission to build without an explicit declaration of gift or ownership transfer: If custom does not indicate that this action is a gift, then it is considered a loan (ariya). Scholars have differed on the fate of the construction in a loan; some believe that the owner cannot evict the borrower except after giving him the value of the standing structure, while others believe that the owner has the right to demand the borrower demolish his structure if that was stipulated. It is advisable to present the matter to an Islamic judge for a ruling.