Το πάτωμα is the bottom part of έναν όροφο, right?
Correct, and there is no limit to how high or how low ο όροφος would be. So it could even be the basement floor.
a native speaker , please enlighten me , which one is correct : βρόμικος or βρώμικος because I`ve seen an article sustaining the first one and stating that the second one is wrong to use , but I see Duo uses it a lot
It's more of a dilemma if you ask me. Some sources state what you wrote, but the spelling "βρώμικος" is incredibly common.