A son built a cottage on a plot of land belonging to his mother.

Answer

The son's house on his mother's land is just like his vehicle is parked on someone else's land. The construction of the house does not make the son the owner of the land. The land remains the property of the mother.

It is the mother's right to ask him to remove his building by demolishing it. Alternatively, he can sell the building to his mother. Or his mother may make a gift of the plot of land to her son, or sell the land to him.

The vacant cottage does not belong to the mother. It belongs to the son. The son has to enter into a rental agreement with his mother. He has to pay rent for the use of the ground. Thereafter he can hire it out and collect the rental for himself. But he has to pay his mother rent for the plot. However, if his mother waives the rental, then it will be permissible.

If the mother had allowed him to build his house without a rental agreement for the plot, then rent is not incumbent on the son. On the other hand, if a rental was stipulated, then he has to pay it. It is Waajib to resolve the issue before the demise of his mother otherwise he will have a serious problem on his hands after her passing away. The land will belong to her heirs while the building on it will be his property. The heirs will be entitled to ask him to demolish the cottage.