Hello Guys, im FancyFloppes and currently Plat on EUW.
Im playing Khazix very frequently in the last time, which my depends on the Youmuus rework, and want to show you which items/playstyle worked out best for me.
I hope my little guide can help you out and im looking forward to incoming armor pen items that just got announced.

Start at Gromp, because Khazix doesnt really profit from the Golems Buff.
Another reason is, that Gromp is a single target Mob and you deal way more DMG with your Q.
You normally go base in lvl 2, after you killed the Blue Buff and Buy the "HUNTERS POTION".
In Patch 5.23 his base Armor was buffed for better early game jungling, but he is still pretty weak in his early minutes, so you always need to care!

After that you should Jungle and help out lanes until you have 700G to buy the "STALKERS BLADE"
and maybe "BOOTS".

After you finished the "WARRIOR ENCHANTED STALKERS BLADE" the party can start, because you deal Massive DMG to your enemies.

CARE: Khazix is really weak in the first 5 levels.

EVOLVE Q FIRST for executing enemies easily and faster objectives!

When Warrior is finished go straight for BOOTS and YOUMUU'S GHOSTBLADE!
Ghostblade is really really strong right now, so just use it as long as you can.

Have Fun and harrass your enemies c:

DONT BE AFRAID OF INVADING ENEMY JUNGLE!
especially when you are lvl6 and u catch the enemy with low hp!!