All perfect praise be to Allah, The Lord of The Worlds; and may His blessings and peace be upon our Prophet Mohammad and upon all his family and companions.
Apartments that have been built for trade are considered from the articles of merchandise liable for Zakah after one full lunar year passes over possessing them. Unsold apartments should be assessed in accordance with their market value on the day they are liable for Zakah, not according to their cost value. Afterwards, the company`s cash amounts and debts immediately due on clients are added, then (2.5%) from the total is paid as Zakah.
As regards apartments sold by installments, Zakah is due on installments against every deferred year; however, it isn`t an obligation to pay their Zakah, save upon collecting each installment. Therefore, it is permissible to calculate the Zakah for one year and pay it from the money in his(giver) possession, or delay that till the collection of each payment and pay its Zakah according to the percentage due on it.
It is worth mentioning that it isn`t permissible to deduct the amount of the debt due on the company from its capital which is liable for Zakah.
It was stated in "Umdat Assalik(98)", a Shafite book, "If he possessed only the Nisaab and was indebted for an equal amount, then he is obliged to pay Zakah, because debt doesn`t absolve a person from paying Zakah." And Allah knows best.