IntroductionHi, i would firstly not recommend this for ranked as it is untested for ranked.
Secondly, this is the way i build him if there is any better item you think would fit, then put them on your build in-game or suggest one in the comments.
Jungling Line-upJungle line up from start to finish camps
Start wolfs>blue buff>wariths>wolfs>red buff>golems(depending on health)>gank top>gank mid or bot.
(includes counter ganking if needed to stop at the golems and quickly gank you can come back to them)
Early GameI would start my early game (winning and made a few ganks and cleared the jungle enough to go buy) with either a bruitilizer and Madred's Razors also boots of speed.
You can go and sell Hunter Machete and go for a health crystal if you have evolved you w first.( id recommened a w first for faster clearing in the jungle / the aoe slow)
Mid GameBy now you should have most of the build complete, if you feel you dont have enough dmg with the maw, than you can sell it and switch over to Blood thirster, depending on how much hp and dmg the ap carry or double aps are doing(top ap player like akail or something).
if they are putting out about as much dps that you are you can go ahead a build the GA for the quick armor and revive.
About your second evolve point, i would put them into the E as the quick resets gives you an better escape/chase.
Late GameSo now the build is complete or almost there, i know i included the black clever but last whisper can be useful against stacked armor champs late game(200 armor+). i haven't tried it yet But i doubt it will let you down
Now the last evolve point would more likely go into the 'Ultimate', some don't even evolve the ultimate i fined it allot better for back-dooring late game which is mostly what you're going to be doing as kha'zix.(mostly anyways)
Final CommentsYou can go tele/smite and do better ganks bot and quick as in a multi-gank situation(from top to bot or mid)