Okay first of all this the 1st build I am posting. The reason I built Kha'Zix like this was acctually kind of simple. Kha'Zix is an squishy Assassin champion and I mainly recommend him to jungle depending how you like him ofcourse.
I have picked these Runes because he needs alot of damage against the Golems and so on to survive. Reason I picked "Greater Quintessence of Strength and Greater Mark of Strength" was that it gives good amount of AD and you can damage monsters easily. The reason I picked the "Greater Seal of Resilience" that Kha'Zix would be taking alot of damage in early game "ALSO" in late game depending how much the enemy team is fed. And last of all the reason I picked "Greater Glyph of Shielding" was that it has an amazing effect that it helps you to build your late or mid game AP resist. The reason that I like the Magic Resist per level is that in early game ofcourse you can deal damage and take no damage in early game. But in late game those champions such as Veigar, Karthus, Ahri and so on will be building AP items as they get farmed and you would need to have more AP resist in late game.
I thought these masteries would make sense to me since a usual team fight is usually 3-AD 1 Support, 1-AP. Hardiness helps in early game for defensive purpose and Durability+Veteran's Scars helps survival chances in early game. Since the champion is squishy as an AD-carry I decided to make an 21-9-0 build and almost exactly alike an AD-carries build.
Reason I picked these items were that he could easily deal damage. I wanted to make it obvious that he is a squishy character and he needs good amount of resistance. People say the Bloodthirster would disable the effect of Maw of Malmortius. Well I certainly disagree. I use it for its Magic Resist and its awesome Unique passives. When you realize your HP is below 30% the Unique passive becomes active and if your opponents HP is higher then you or the number of opponents is more then you such as 2 vs 1. It allows you to run away. By the way you buy the potions even if you got the full build or no space at all. The Second you buy it gets activated.
I recommend to build "Taste their fear" 1st since it is Kha'Zix's main damage source. Many people likes to build "Void Spike" but I especially recommend to level up "Leap" before "Void Spike". The reason is that you would acctually want to deal some good damage while jumping and there are chances of missing the Void Spike since it is a skill shot though also has burst damage. By missing not that im insulting or anything I mean that there are chances of mouse sliding, lag, and so on. When you come to Level 6 with Kha'Zix. I recommend to Evolve "Leap". It allows you to jump further and gank better. Especially after kill when the cool down resets you can jump to the next target and kill him as well if you are lucky. When you become Lv 11 I recommend to Evolve "Taste Their fear" which gives massive amount of damage if the enemy is even building a tank. For Level 16 evolve I mainly recommend to evolve the Void Assault. It can be used in offensive way to make the passive active and to run away purpose if the team is failing or you are entering a 1 vs 5 combat.
The reason I pick smite and Flash is simple. Flash can be used in offensive way which I do not recommend usually but if a successful kill then you can use the Evolved Leap to run away if someone is trying to gank you when you are in low HP. Also the reason I pick smite is not only that you can jungle faster but you can steal or kill Baron Nashor or the Dragon faster. People think that is useless but using Void Assault you can steal the Baron Nashor or the Dragon and then run away by using the Leap or your Flash.
Pros / Cons
The champion makes very good damage
Can easily run away
Has big advantage in 1 vs 1 battles.
Champion is almost immortal if fed well
Champion is squishy at beginning
Without his blue he will have difficulty jungling
Has difficulty ganking in early game.
Creeping / Jungling
I recommend normal jungling such as starting with Blue, heading to wolves, then going to Wraith. If you have enough HP you should do the golems without using your potion. If you do not have enough HP then you should just go back to base and refill your HP. Your blue should stay until you kill the Golems and get the Red. After you get the red you can easily gank and do not forget to use your basic attack. It slows down people and deals good amount of magic damage.
This is about it. Like I said this was my 1st build so I couldn't add pictures (most likely I don't know how to). But if you can check out the things I have written then I recommend try this build. I know it would of been easier if I have added pictures but I am honestly bad with the codings and so on. I hope you like the build ^_^.