Is Zakat obligatory on rented or empty houses, at what price is the Zakat estimated, and should the property be sold to pay its Zakat if money is not available?

If the houses are prepared for rent or for personal use and not for trade, then there is no zakat on them. Zakat is only due on their rent if it reaches the nisab and a full year has passed. However, if the houses or part of them are prepared for trade, then zakat is obligatory on them as trade goods. These goods are appraised at the time zakat becomes due, and a quarter of one-tenth (2.5%) of their value is to be given. If zakat becomes due and you do not find money to pay it, then you must sell a portion of the goods to settle the zakat, provided there is no harm in doing so. Otherwise, it is permissible to delay it until liquidity is available.