like the first floor, second floor etc? Piętro is more common, kondygnacja is technical word.
We call the ground level - parter, and level/floor above it 1 piętro.
Language trivia, this time about English: "ty" in some casual text communication is used as an shorthand of "thank you". The first time I saw it a few years ago I thought somebody was actually trying to address me (in Polish).
Probably no one. Unless someone enjoys lying on someone else's floor, does it often, and therefore literally 'likes it'.
"Podoba mi się ich podłoga" would mean that the floor is... well, nice-looking, and makes a lot more sense.