For example when you say about dates or you want to number something like in English: sixth, seventh, eighth.
"podłoga", as 99% of nouns ending with -a, is feminine: ósma.
However, "podłoga" means "floor" literally as the thing on which you are standing in your room. Or on which your carpet is.
"floor" as is "8th floor of a building" is "piętro" and it's neuter: ósme piętro.