This is meant as my own personal reference for jungle Kha'zix but people are more than welcome to give their own tips and advice. I have no clue how to format guides or any of that fancy stuff, sorry, but I will do my best to give some information regarding my choices. Happy Hunting.

Pros:

Good Jungle
Great Skins
Evolves!!!!
Capable of Massive Damage
Great Ganker
Very Powerful in Team Fights
Very Fast
Very Large Melee Range

Cons:

Really Weak Early Game
Squishy
Base Attack Damage does not Count Towards his damage bonuses

As far runes go I cannot stress enough that you MUST have some attack damage (I recommend marks) because as stated above your base attack damage is not counted when figuring out your bonus damage on abilities.

Other than that I just prefer defensive Seals and Glyphs but on account of his squishyness I do highly recommend them.

Viable quints that aren't Movement Speed are Crit Damage, Attack Damage, or possibly Intellect if you get particularly mana starved early game.

Masteries are really very basic ADC masteries, not much to be said here. Feel free to fiddle with the points in defense.

Cloth Armor and five pots, tried and true opening. Then I go boots and a Mana Crystal. Even though I wont be building Sheen until later on it does help from getting mana starved. After than I build an Infinity Edge (for the AD and Crit). Next is a Triforce the only thing here is to build Sheen and then go Phage. Next is a Bloodthirster as it will help you with late game exchanges and it has a lot of AD. At this point it'll be pretty late game so the last two Items are really personal preference and/or what you need. I like Phantom Dancer for its movement speed and it basically guarantees crits. And I like the Black Cleaver because its good in team fights, 1v1, and has a lot of AD. Maw of Malmortius would also make a great last item.

I know this build takes a lot of feeding but once you have just infinity edge and triforce you should be in really good shape with this champion.

When Jungling make sure to take your W (Void Spike) as it is a ranged, small AoE damage, skill shot that will heal you if you use it in melee range. This means that when you are taking blue or meleeing that champ you can cast W and heal yourself for a good amount early game.

The thing you should be alternate leveling with your W is your Q (Taste Their Fear) it works as a single target, melee range burst. It will also mark targets that are alone (Champions that aren't near their own minions, structures, or team mates). The marker means that your Q will deal extra damage to that target.

After that is your E (Leap) this allows you to jump to an area and deal a small AoE. This is a great utility skill for initiating ganks, chasing, and getting over walls while fleeing.

And finally is the Ult (Void Assault). This ability allows you to stealth for one second, in which you gain 40% movement speed, and it resets your passive. But this doesn't just happen once, nope. About 2 seconds after you come out of your first stealth you can cast in again within a 10 second time frame and steath again.

The real reason were all playing Kha'zix. Every time he takes a rank in his Ultimate he gets an evolution point which allows him to make one of his skills even better.

If he evolves his Q, WHICH YOU SHOULD ALWAYS DO FIRST, he will get an increased melee range as well as an increased range on his Q.

If he evolves his W his W will shoot two more projectiles in a cone like fashion (three in all) and slow the enemys who are hit if you had your passive available.

If he evolve his E you will get an even larger jump range and when you kill or assist in killing an enemy champ the cooldown on your jump will reset.

AND IF YOU ARE CRAZY ENOUGH TO EVOLVE YOUR ULTIMATE! You will change color. And be able to cast your stealth three times in a row as opposed to two. And you will also take 40% less damage while in steath (not counting bushes).

Blue (have someone leash)
Wolves
Wraiths
Red
Gank bot or mid (try to secure a kill)

After here you can run around pretty willy nilly. Just keep these rules of thumb:

Kill wraiths when they are up
Kill wolves when its convenient or when you are bored
Gank a lot
Keep up with Red and Blue
Be kind enough to hold lanes for people sometimes

Kha'zix is a great champ with a high skill cap. He is very fun to play and takes a lot of practice to get perfect. Roll some heads guys, happy hunting!