He has a share in some commercial land – how should he pay zakaah?

Zakaah must be paid on
things that are prepared for sale or trade (land and other things) when one
full year has passed since the time when they were prepared for sale. The
way in which the zakaah is calculated is to work out the value (of the land)
when the year has passed, and pay one-quarter of one-tenth of the value as
zakaah. 

The scholars of the Standing Committee said: 

Zakaah must be paid on lands that are prepared to be bought
and sold, because they come under the heading of trade goods, so they are
included in the general meaning of the evidence in the Qur’aan and Sunnah
that zakaah is obligatory. Allaah says (interpretation of the meaning): 

“Take Sadaqah (alms) from their wealth in order to purify
them and sanctify them with it”

[al-Tawbah 9:103]

Abu Dawood narrated with
a hasan isnaad that Samurah ibn Jundub (may Allaah be pleased with him)
said: The Messenger of Allaah (peace and blessings of Allaah be upon
him) commanded us to pay sadaqah (i.e., zakaah) on that which we had
prepared for sale. 

This is also the view of the majority of scholars, and it is
correct. 

Fataawa al-Lajnah al-Daa’imah,
9/331 

It makes no difference if
the land is owned entirely by the one who is paying zakaah or if it is
shared out as when many people hold shares in it. 

The scholars of the Standing Committee also said: 

The Standing Committee was asked about zakaah on lands that
are owned through shares – is the ruling on these the same as the ruling on
trade goods or the ruling on real estate?  

They replied: 

If a person acquires real estate with the intention of
trading it (selling it later on to make a profit), whether it is shared or
he owns it outright, then the ruling is the same as the ruling on trade
goods, and zakaah must be paid on its value if it reaches the nisaab
(minimum threshold at which zakaah becomes due), when one year has passed.
The way in which the value is to be worked out is to estimate its value at
the end of the year, and this estimate must be done by one who has
experience in that field.  And Allaah knows best. 

Fataawa al-Lajnah al-Daa’imah,
9/326 

And Allaah knows best.