Does zakat include commercial store displays, libraries, student services, and buildings under construction?

Zakat (definition) is due on all goods and items prepared for sale and trade, such as school supplies, with the exception of the premises and tools used not for sale. However, if buildings are not for trade, there is no zakat on them. But if they are rented out, then zakat is due on their earnings if a year has passed over them and they reach the nisab (definition). If they are for trade, then zakat is due on their current value upon the completion of a hawl (lunar year) on the capital.