Is it permissible for a man who owns a commercial plot of land and has a salary that suffices him and his family, and lives in a house belonging to the state for a nominal rent, to take from Zakat funds, knowing that he cannot buy a house even if he sells the commercial plot?

It appears from the questioner's situation that he is not eligible for zakat, because he finds enough to support himself and his dependents. A rich person is not eligible for zakat, due to the Prophet's (peace and blessings be upon him) saying: "Charity is not permissible for a rich person, nor for one who is strong and able-bodied."

The richness that prevents one from receiving zakat is that which provides sufficiency. So, if a person is not in need, charity is forbidden for him, even if he owns nothing. But if he is in need, charity is permissible for him, even if he owns a nisab (the minimum amount of wealth subject to zakat).

Land prepared for sale is subject to zakat if a year has passed over it and its value reaches the nisab.