Recently there have been some questions here about two-storeys, etc. I have always been under the impression that in Europe, the ground floor is the ground floor, and the one above that is the first floor. (Or storey.) Is that true?

If that's so, and you say "it's a one-storey" building - it has only a ground floor/storey? But if it's "two-storey building" it has the ground storey and the first storey?  Like, would you say "His flat is the entire first storey of a two-storey building" to mean to he lives upstairs? I'm sorry to sound like a dumb American here, but this has always puzzled me.

And once and for all, is it a three-storied house or a three-storey house or a three-storeyed house?

And do Brits use the word "floors" at all to refer to the levels of a building? (Not that thing we stand on.)

So I know our teaching buildings adopte the so called "European floor counting system", i.e. before we see the signs of “1st floor”, we have to climb up two flights first. The ground floors are just parking lots (I don't know the exact English name for these large lots without doors but with short slopes at the entrances) full of students' bicycles and senior teachers' cars.