Where do you get the word "story" from? The recommended translation for the sentence is "Have you washed the floor?" with "floor".
However, llawr can also mean "story" in the sense that is also spelled "storey" -- a level in a building. For example, a three-storey house (or three-story house) could also be called a house with three floors. Depending on where you are from, you might call them ground floor, first floor, second floor; or first floor, second floor, third floor.