I can't beat ghetsis I've tried 15 or so times. Can you help me?

You trade people level 100 Pokemon and you will be able to beat the league.

I just purchased 50 or so revival herbs from the market in driftveil

Your Pokemon shouldbe at least about level 60 or so tobeat him, it depends on how well you battle and type,moves ect. If you need strong Pokemon I would be sending you Here witch is the SuperCheats Pokemon trading forum where you can start a topic requesting whatever Pokemon you would need.

Dont listen to mewthree. I beat him with only a couple Pokemon at around level 50. Here is my team so you know what I used:
Lvl 52 Servine
Lvl 53 Conkeldurr
Lvl 50 Zekrom
Lvl 50 Swanna
Lvl 46 Victini(optional; helped me with elite 4)
Lvl 41 Krookerock(<- sorry forgot name; evolved form of krokorok)

My team was:
Zekrom lv. 50
Mienshao lv. 52
Excadrill lv. 50
Darmanitan lv. 51
Braviary lv. 54
Samurott lv. 55

My team sucks but I still beat him. Here are the Pokemon that I used:Zekrom lv50,Emboar lv67,Sawk lv49,Mienshao lv60,Conkledurr lv53 and a Beartic lv59

My Pokemon and tactics
Level 58 Haxorus
Level 56 Emboar
Level 51 Zekrom
Level 37 Boldore
Level 31 blue turtle Pokemon thingy (not squirtle something else)

Teach Emboar, boldore and turtle bulldoze.
Use Haxorus with Cofagrigus first. Use dragon claw, maybe twice

When Hydreigon comes out use boldore with bulldoze. His sturdy ability will keep him from dying. Same with turtle. Use emboar with bulldoze next because he won't die in one hit even with surf which he's weak to - too much health.

Hydreigon's health is lowered now so use haxorus with dragonclaw and he should strike first and OHKO him.

Then use haxorus swords dance and sweep the rest with dragon claw.

I had a 50 Samurott with Dragon Tail, a lvl 50 Cincinno, lvl 52 Haxorus, lvl 50 Archeops, lvl 54 Zoroark and a lvl 50 Zekrom.

You can easily whittle down Cofagrigus with Zekrom with repeated Dragonbreaths.
Boufflants not too hard to take down although watch out for it's Head Charge.
Bisharp falls VERY fast to fighting moves so take advantage of that.
Seismitoad is fairly annoying, it's fairly beefy and can hit decent amounts of damage.
Eelektross shouldnt post too much of a threat, I used Zekrom as a form of resistance and spammed Dragonbreath on it.

Hydreigon is the one you should be worried about. Having fairly high speed and sp atk, it can deal devastating damage similar to how Cynthia devastates your team with her Garchomp.
My tactic was relying on my Samurotts Dragon Tail which deals damage and knocks it out of the field. Once Ghetsis's other Pokemon egts sent out, that's when I take advantage in healing my Samurott.

Well thats all I have to say, good luck on Ghetsis

I feel you. I haven't beat him but I sugjest leveling your Pokemon up at route 10 or at 9. Hope this helps. ;p