Sheikh `Abd al-Wahhâb al-Turayrî, former professor at al-Imâm University in Riyadh
You do not have to pay Zakâh on the plot of land where you are building your house.
As for the other plot of land, if you intend to use it as a source of income, then you have to pay Zakâh on it; otherwise, you do not.
And Allah knows best.
Source: Islam Today