Mi ne komprenas la diferencon inter "pluraj" kaj "multaj"
pluraj = an undefined number, more than one (several),
multaj = a large undefined number (many, much).
Is "plankojn" not equivalent to "stories" as well as "floors?"
Not according to the definition of planko.
Here, English uses the same word for two different things, but that's not the case in some other languages: