Is Zakat annually obligatory on money collected for building and furnishing a house, and does the ruling differ if the work stops and the collected amount decreases?

Zakat (definition) must be paid on money if it reaches the nisab (definition) (equivalent to approximately 595 grams of silver or 85 grams of gold) and a full lunar year has passed, even if it is saved for building a house. Provision is in the hands of Allah, and zakat increases wealth and blesses it, as Allah Almighty said: "And whatever thing you spend [in His cause] – He will compensate it; and He is the best of providers," and the Prophet, peace and blessings be upon him, said: "Charity does not decrease wealth."