Is it permissible for a father to suggest to his son building an additional floor on his own property, and then registering it in the son's name, knowing that the property will devolve to all heirs after the father's death, and that this suggestion might provoke the anger of the rest of the siblings?

If a father permits one of his sons to build on his land, this is a gift of the land's airspace, and it is permissible if there is a legitimate reason for singling out this son, such as his need for housing, illness, a large family, or preoccupation with seeking knowledge. If the father intends thereby to meet the needs of his needy sons without preference, then there is no harm in that. Ibn Qudamah said: "If he singles out some of them for a reason, such as singling him out due to need... it has been narrated from Ahmad what indicates the permissibility of that, for his saying regarding singling out some of them with a وقف (endowment): 'There is no harm in it if it is for a need.'" Kinship ties with the brothers should be maintained.