I agree with Ronald Sole's answer, but I have something to add:
Come up to the third floor.
This is fine.
Which floor is it on?
This is fine.
Which floor do I come?
You could say which floor do I come to? or, if you're feeling pedantic or snooty, to which floor do I come? But I would more likely say which floor is it on?
I was in a hotel and my room was on the fourth floor. I wanted a top floor. Not the very top but I just wanted to ask if other floors are available. I said:
Can we get a top floor room. (I'm sure it's incorrect)
If you want a floor near the top, but not necessarily on the top, you could say can we get an upper-floor room? Alternatively, you could say could we get a room on one of the upper floors? or could we get a room on a higher floor?
(Note the use of conditional could, which is slightly more polite -- I actually didn't even notice I changed to could until I proofread that paragraph. Other formulas are of course in use, such as would it be possible to ....)
Finally, again on proofreading, I notice that your room was on the fourth floor. If you were in fact on the fourth floor, you would not say come up to the third floor but go down to the third floor.