What is the ruling on a father writing the house, in which the questioner built the second and third floors, in the questioner's name without the consent of his siblings, knowing that the questioner financially assisted his siblings?

The fundamental principle is the obligation to be just among children in giving gifts. However, favoritism is permissible if there is a valid reason, such as need, virtue, or righteousness. If your father's preference for you is due to your financial assistance to him in construction and expenses, this may be considered a valid reason that permits him to gift the house to you. There is no harm for him in registering it in your name, even if the other children are displeased. Nevertheless, it is recommended to attempt reconciliation among siblings and avoid anything that leads to discord.