Hey, this guide isn't done yet. Or even close to being done at this point. Stay tuned for updates.
I will probably switch to electrocute, and I might even go off of Tiamat depending on how hard the nerfs are.

Update: I still love tiamat, dark harvest sucks, I run electrocute now.
Update 2: Overall, not much has changed. Crab changes were super strong for Kha'Zix, I will be updating clear path section soon. Kha is in a fantastic spot with new crab changes.

I evolve QEW. Every game. QEW is the strongest evolution order for Kha'Zix individually. W evolution level 11 gives his team an advantage, but E is far stronger for Kha'Zix. Why does Kha'Zix need the individual advantage vs team advantage? Because it's SoloQ. You can't trust the robots in your games to do anything even remotely resembling intelligent play, regardless of the elo you find yourself in. Q evolution gives you huge dueling power, makes your QE buffer faster, increases your kite range, gives you much higher DPS for neutral objectives, higher clear speed, among many other things. As a second evlution, E gives you 1v9 potential in teamfights. Utilizing his resets, Kha'Zix can easily make short work of a team by picking off backline carries and key members of the opposing team. As a third evolution, W gives Kha'Zix lots of artillery damage and keeps him relevant in the late game with big poke and a 90% "slow"(root) for 2 seconds.

(NOT ACCURATE FOR PATCH 9.7)

Okay, so Kha'Zix goes either Hunter's Machete or Hunter's Talisman depending on what his first clear is. If Kha'Zix is Blue Side(meaning red buff is bottom), I prefer to go Hunter's Talisman and do Red>Krugs(smite big Krug)>Raptors, then either full clear or gank mid, depending on the volatility of the lane and whether or not I think there is any kill pressure(more on that later). On Red Side(blue buff is bottom), I go Hunter's Machete and do Blue>Gromp>Wolves(smite wolf)>Red buff> Gank top/mid/take skuttle. Whether I gank top/mid or go for skuttle is situational and depends on how volatile the lanes are and the kill pressure I believe we would have(again, I'll go more into detail in later chapters).

Death's Dance is a good replacement to Warrior after full build. Quicksilver Sash for Malz/Lissandra/point and click hard crowd control, if they have a fed Karthus, or Syndra or someone who has lots of unavoidable damage, get Hexdrinker. Black Cleaver is great into 2-3+ tanks, Mortal Reminder for excess healing. Edge of Night and Ravenous Hydra are your two replacements for Tiamat when full build, and it all depends on the game. I normally take Ravenous, but Edge of Night is useful into champions where they often need to hit a core ability to set you up with their full combo, like Twisted Fate, or other such champions. Do NOT replace Quicksilver Sash for Edge of Night. If you built Quicksilver Sash, upgrade to Mercurial Scimitar, and if you built Hexdrinker upgrade it into Maw of Malmortius. Upgrade Mercurial Scimitar after your core is completed, but if the magic damage is very threatening, you can finish Maw of Malmortius.

While in the Item Set tab, you can choose to paste a copied set. Here is mine:

{"title":"kha full","associatedMaps":[11],"associatedChampions":[121],"blocks":[{"items":[{"id":"1041","count":1},{"id":"1039","count":1},{"id":"2031","count":1}],"type":"first"},{"items":[{"id":"1036","count":1},{"id":"3133","count":1},{"id":"3706","count":1},{"id":"1400","count":1},{"id":"1001","count":1},{"id":"1029","count":1},{"id":"1033","count":1},{"id":"3158","count":1},{"id":"3111","count":1},{"id":"3047","count":1}],"type":"recall"},{"items":[{"id":"1036","count":1},{"id":"3077","count":1},{"id":"3134","count":1},{"id":"3133","count":1},{"id":"3147","count":1}],"type":"postwarrior core"},{"items":[{"id":"1036","count":1},{"id":"3035","count":1},{"id":"1037","count":1},{"id":"3036","count":1}],"type":"postcore-ldr"},{"items":[{"id":"1036","count":1},{"id":"3134","count":1},{"id":"3133","count":1},{"id":"3142","count":1}],"type":"postcore-gb"},{"items":[{"id":"1036","count":1},{"id":"1037","count":1},{"id":"3134","count":1},{"id":"3133","count":1},{"id":"3812","count":1},{"id":"3814","count":1},{"id":"3074","count":1},{"id":"2140","count":1}],"type":"final+other options"},{"items":[{"id":"3155","count":1},{"id":"3140","count":1}],"type":"anti-ap"},{"items":[{"id":"3071","count":1},{"id":"3053","count":1},{"id":"1412","count":1}],"type":"bruiser variation(suboptimal)"}]}

https://twitch.tv/produx2/
https://discord.gg/UDqXYpv

I'm pretty active in my discord, hit me up if you got any questions about Kha'Zix.

So one of the biggest questions I've been getting asked was "Why take Tiamat?". There are a few answers, but a lot of it boils down to preference and what you specifically want to do. It does more damage than dirk with even low AD(it gets better vs tankier targets and higher AD), but is *slightly* less efficient, while also contributing to faster clear speeds, allows you to easily get isolation in minion waves, among other things.