First, take off all your strings. Than *very* carefully check for unlevel frets. Good?
Now put your strings back on, tune that sucker up and slap a capo on the first fret.
Now check the relief, it should be just a hair in the middle of the neck. Still buzzing?
Now you need to measure the action at the 12th fret if you want us to help you better than giving vague advice.
Measure the action at the 12th, and 24th fret where you think it feels good, and than raise the bridge until it doesn't buzz than take those two measurements again.
Do those things, than we can help you better.
As I'm sure you already know, when doing the setup it is very important to do everything perfectly, and in the right order. For instance, if you try to set the bridge height without first setting the nut height your just going around in circles...
I'm going to run through how I check certain things just to give you can idea of something you might be missing.
(this is assuming that the frets are *perfectly* level already)
First comes the nut:
How do you check nut height? You should press down between the 2nd and 3rd frets and check the distance between the string and the first fret. It should just *barely* be above the fret. If it's touching it's too close, if it's more than just a hair it's too far.
Than comes relief:
Hold down the string on the first fret, and the last fret (in your case 24) now measure (I usually do it by eye) the distance between the string and the 8th-12th frets (rough area, will change depending on how many total frets are on the guitar). It should be just a hair, enough to where you can see light underneath the string, but as small a space as you can get it.
Next comes bridge height:
I have measurements that I use to get it in the ballpark of where I want it, but since you don't have anything to measure it with I'd recommend starting with a high action, than bringing it down bit by bit, until it starts to buzz, than back it off just a tiny bit.
There you go thats the lowest action that guitar can have without buzzing.
Than it's on to intonation which I'm sure you already know how to do so I won't cover it.
I hope that helps, but like I said, without measurements all we can do is offer vague advice...