How is zakat calculated on a three-story house with a shop (the first floor is for the mother's residence, the second for the questioner's residence, the third under construction for future rental), a car for personal use, a summer apartment for personal use, a plot of land for sale or building for investment, and a four-story house under construction (the first for residence and the rest for sale or rental for investment)?

There is no zakat on real estate intended for residential use (floors of houses, a vacation apartment), nor on a car for personal use. A rented commercial property has no zakat on its intrinsic value, but rather on its rental income if it reaches the aformentioned threshold and a year has passed over it. As for a plot of land and other floors under construction, for which no definitive decision has been made to sell or invest them, there is no zakat due on them.