He bought some land in order to sell it after a while – how should he pay zakaah on it?

If a person has bought land with the intention of selling it
after a while, one of the following two scenarios must apply: 

1 – He aims to save the money so that he will not spend it on
anything else, but he does not intend to trade or make a profit. In this
case there is no zakaah on the land. 

See question no. 34802 

2 – He does intend to trade and make a profit, in which case
this land comes under the heading of trade goods, so zakaah must be paid on
it. 

The value of trade goods should be worked out at the end of
one year on the basis of their current value, not the price for which they
were bought, and the zakaah must be paid on them. The rate of zakaah that
must be paid is one-quarter of one-tenth, i.e., 2.5%. 

For example: if you bought land for one hundred thousand
riyals, and when zakaah becomes due on it its value is now one hundred and
fifty thousand riyals, then when one year had passed you must pay the zakaah
of one hundred and fifty thousand riyals. The converse also applies. If you
bought it for one hundred thousand riyals and when one year has passed its
value is now only fifty thousand riyals, then you only have to pay zakaah on
fifty thousand riyals. 

See Fataawa al-Lajnah al-Daa’imah, 9/334; Fataawa
wa Rasaa’il al-Shaykh Ibn ‘Uthaymeen, 18/205, 236 

Note: 

It should be noted that
the year for reckoning zakaah on trade goods does not begin from the time
one bought the land or other product, rather it begins from the time when
the wealth with which you bought those goods reached the nisaab (minimum
threshold).

 Based on this, the year for this land is the year for the
money with which you bought it. 

See question no.
32715.