Is Zakat obligatory on a plot of land purchased with the intention of building on it, and does the ruling differ if it is sold or invested, and is it recommended to spend in charitable causes as a good omen for future building on it?

The land you purchased with the intention of building a house for residence is not subject to Zakat, because it is for personal use and acquisition. This is based on the saying of the Prophet, peace be upon him: "There is no sadaqa (Zakat) on a Muslim regarding his slave or his horse." There is also a consensus among scholars that assets acquired for personal use are not subject to Zakat.

If the land is sold and the price is received, and the price, or part of it, remains for a full year and reaches the nisab (minimum threshold) by itself or when combined with other assets, then Zakat becomes obligatory on it.

The Shari'ah encourages giving charity at all times, and it is one of the greatest acts of worship, as Allah Almighty says: (Who is it that would loan Allah a goodly loan so He may multiply it for him and he will have a noble reward). And the Prophet, peace be upon him, said: "Give in charity, for charity is your release from the Hellfire." It is prescribed to give charity with money when building a house or for any other purpose, with the intention of providing for the needy, out of joy for Allah's blessings upon you.