Use the noun razing when you talk about the utter, total destruction of a building. The razing of your old elementary school might bring tears to your eyes.
When a house is knocked down, flattened by a bulldozer, you can say it's been razed. The act of this happening is a razing. The razing of whole cities can happen during war, when bombs destroy blocks of buildings. Your dad might order the razing of your childhood treehouse once it's gone unused for years. The verb raze was originally racen, "to pull or knock down," from the Old French raser, "to scrape or shave."