This will be my first guide and also probably my last one. Anyway Kha zix is a melee assassin, there's not much to say about him besides the fact that he is very similiar to rengar. So yeah if you play him well he could be anoying as ****.
Also if you happen to play against an enemy team which happens to have a rengar you will unlock a bonus quest saying that whoever (Rengar or Kha zix) slays (or an assist) each other first will receive a bonus. If you clear this bonus quest while being Kha zix you will be able to evolve one more time.
If you do not agree with anything wich is being said in this guide, than...you're probably right. But I'd like to give my opinion and here it is.

Kha zix isn't very storng early game. Which makes sense since he evolves overtime, making him very good late game. That's why I chose to have these runes which make his survivability a bit better in the jungle early game, also this wil cause him to deal lots of damage early game while ganking, making it a lot easier to pick up some kills.
While Kha zix is very good one on one, he's not that great in a teamfight. Since Taste their fear deals the most damage of all Kha zix's abilities and works best when a enemy champion is isolated. Also Kha zix will mostly be focused in a teamfight (next to the AD carry) since he can deal tons of damage when left undealt with. That's why I take magic resist per level so that champions with a lot of CC won't be able to completly disable Kha zix in a teamfight.

If you're here to look for a build which explains how to play Kha zix AP well than good luck to you, because Kha zix is really at his best being an AD champion. That's why i chose these masteries, dealing tons of attack damage en sustainability early game.

When jungeling with Kha zix please take the items I recommended, in my opnion they are the best to bring out his full potential as a melee assassin. The only thing you might consider not buying is the Last Whisperer. The last whisperer is a very handy item, since it gives you a lot of attack damage and armor peneration something which is key to unlocking Kha zix's true potential. Being able to give great ganks and dealing tons of damage in just a couple of seconds. However when you're up against an enemy team which doesn't have a lot of armor stacked up you're best choice for your last item is to take a Hextech Gunblade. Giving Kha zix even more attack damage and life steal (the amount of ability power and spellvamp you receive by buying the Hextech Gunblade is a nice little bonus) making him an almost impossible foe to take on on your one.

Since this is a guide about how to jungle with Kha zix the first summoner spell and the most logical one is smite. Please do me this favor and take smite if jungeling. With any jungeler!
I chose flash as a second spell because flash (if used properly) is a really great escape tool, as well as being a quick way to close the gap between you and "your prey". Since Kha zix can already escape very quickly by using his Leap, this will make sure that enemy champions won't be able to catch up with you.

I won't explain a lot about my skill sequence but i will tell you that you should rush your q. But nobody really wants to know that. What everybody wants to know is what you should evolve and what you shouldn't and in which order. There are two things on which most players agree on. First of all evolve your leap, so that enemy champions have a hard time catching you, seriously this makes the difference between life or death! Also this will make your ganks all that more better since you can leap from a greater distance on a enemy champion and if you're standing under an enemy turret while receiving a kill you will be able to instantly get out of there again since the cooldown on your leap is refreshed.
The second skill that you will need to evolve is Taste their Fear, because this deals the most damage of all Kha zix's abilities and is also the one you will use the most.
This is the part where a lot of people have discussions about and there's not really a right or wrong. The last ability you can evolve can either be Void Spike or Void Assault. It's your choice which one you like the most and play best with. I personally prefer to evolve Void Assault, since this allowes you to use your passive three times in a row, but it's up to you. Perhaps you don't even need to choose and you just have to kill Rengar to unlock your 4th evolution. The hunt is on!