How is zakat calculated for real estate land under construction, with part of its building cost paid and some of its apartments currently being sold, and is it considered trade goods now or after completing construction and knowing the profit?

If the land and its structures are for residential purposes, there is no zakat (definition) on them. If the building is for rent, there is no zakat on its value or on the land itself, but rather on the rental income received from it, provided it reaches the nisab (definition) (minimum threshold) and a full year has passed over it. However, if the land and building are for trade, then they are considered trade goods, and zakat is obligatory on their value every year, regardless of whether there is profit or knowledge of it.