Is an uncle, who gifted the roof of his house to his daughter and her husband, who then built two apartments upon it, entitled to retract his gift and reclaim half of the roof after prices have risen, justifying this by claiming that Islamic law permits him to do so?

If a father gifted the roof of his house to his daughter and then revoked his gift after she had built upon it, or after a third party's right became attached to it, he is not entitled to revoke the gift. Therefore, the father must return the apartment he took from his daughter and her husband due to the enforceability of the gift. It is permissible for them to reconcile by accepting compensation for the construction, with their consent and good will.