This is my new build/guide for Kha'Zix. I hope you'll test and like it. I often had Mana Problems with him so i suggest to buy Sheen. Then I suggest to buy Last whisper a bit later and sell The Brutalizer but optional you could make The Brutalizer into Youmuu's Ghostblade for some crits.

Another optional item purchase is to start with boots of speed and some health potions because Kha'Zix only has a bit more than 500 live points at the beginning and then buy Doran's blade two times.

Instead of ignite you could choose Heal but you should have something about 2000 livepoints so you barely have to heal yourself.

everytime you level up your ulti you are able to make an evolution on one of your spells. I would recoment to power up Void Spikes, Leap and then your ulti Void Assault. But of course you can do it how you want its just a suggestion ;)