Americans always focus on facades, and think about buildings as commodities. The logic is that in the American conception, each floor is a floor-to-ceiling architectural layer, as viewed from the front of a building. So you think:
B2 - Second layer below visibility B1 - First layer below visibility 1 - First visible layer 2 - Second visible layer 3 - Third visible layer
“How many layers am I paying for, when I buy this building? Sir, If you buy 7 layers at this low, low price. I will throw in an 8th layer for free!” “OMG did you hear Frank’s new house has 4 layers! Frank has way more status than Bob and his paltry two layer building.”
Whereas in most countries, the conception is that a floor is each literal floor you pass as you go up or down while traveling inside a building.
-2 - I’ve descended two floors -1 - I’ve descended one floor 0 - I haven’t gone up or down since I entered this building 1 - I’ve ascended one floor 2 - I’ve ascended two floors
I’m an American that lives in Italy about half of the time. I was being facetious a bit, but it is true that there is a cultural differences in how people think about this, it’s not just words. Someone else commented on the German words for it, which (as is typical with German over Romantic languages) is more appropriately descriptive.
“Go up 3 floors and turn left.” in the US would put you on the fourth floor, but in Europe each floor you go up is the number of the floor you are on. It’s more common in the US to say “Go up to the 2nd floor.” unless you’re not starting on the 1st floor.
In Europe if you say “I want a building with 7 floors.” no one will be confused, they will know that you want a ground floor and 7 above ground floors. They would probably also know what an American means when they say it. Only the Americans would be confused and they hilariously are as they look for their AirBnB’s here on vacation!