Is zakat due on money invested in a stalled real estate project?

Real estate intended for investment and trade is subject to zakat by assessing its market value each year. Zakat becomes due when a full year has passed on the original price of the building materials with which it was purchased. As for raw materials intended for manufacturing, such as metals and oils, zakat is due on their market value at the end of the year. However, real estate intended for rent is not subject to zakat on its principal asset itself, but rather zakat is due on its revenue (rent) if a full year has passed and it has reached the nisab. The nisab for banknotes is the equivalent of 85 grams of gold or 595 grams of silver, and the obligatory amount to be given is a quarter of a tenth (2.5%).