My aim with writing this guide is to teach beginners and veterans of LoL alike the abstract art of playing Bruiser AD Kha'zix.
Playing bruiser Kha'Zix is a little different then how he was designed to be played. Normally, as an assassin, Kha'zix is supposed to jump into a team fight and finish off any enemies on low health. A Bruiser, on the other hand, is played by rushing into a fight and dealing as much damage as possible. Playing Bruiser AD Kha'zix requires you to find a careful balance between the two, allowing you to deal a lot of damage and finish off enemies while still being able to take a few hits.
I am by no means a master at LoL, but I have found a few abnormal ways of playing characters(I can play in any position, top, mid, adc, supp or jungle. XD) that work pretty well. Hopefully you will all learn a thing or two about abstract Kha'zix play.

+ Good Damage Dealer + Lots of HP/Armor/MR + Good at picking off enemies + Amazing at Farming + Moderate sustain + Good ranged poke( Void Spike)

- Cooldowns weaken him significantly - Weak to Crowd Control - Countered by early game sustain

Last Whisper

The Last Whisper is one of the best ways to counter a tank in the game. Assuming that the tank is building armor, whisper will negate a lot of the damage reduction that will plague you if you don't get it. It's always a good idea to build the pickaxe first, as it gives more damage per gold then the long sword.

Black Cleaver

Black Cleaver is a good alternative to the Last Whisper. If your opponents aren't building as tanky, the lower armor penetration won't matter. It will also give you some health and a little more damage.

Bloodthirster

Bloodthirster is one of the best damage and lifesteal items in the game. It is rare, but not unseen, for a dual bloodthirster build to be played. If you have enough health/magic resist/armor to last you in a team fight, but your damage or lifesteal is lacking, then getting a second bloodthirster is a good choice. Just remember, in the later game, you may still want more health/magic resist/armor, and you may have to sell one of the bloodthirsters. Buying a second bloodthirster is always a trade off that you have to carefully consider.

Ravenous Hydra

Ravenous Hydra is a good item to choose when you need better sustain during a fight, or more damage. It will help with minion farm as well. When in a fight, it is always a good idea to engage them in the midst of the enemy minions and use the Hydra's passive. The AOE damage will apply on-hit-effects, including lifesteal. This will make it much harder to deal damage to you until the enemy minions die, as you will be taking health from both the enemy and any minions around them.

Randiun's Omen

Randuin's Omen gives you a great deal of both armor and health. It has a good passive and a good chase or escape active. It is always a good idea to build this if you started with the cloth armor VS AD build, as the wardens mail builds directly into it. Even if you didn't start VS AD, if you need health or you're taking a large amount of AD damage, it's good to pickup.

Guardian Angel

Guardian Angel is almost a core item. It gives a large amount of both magic resist and armor has one of the most useful passives in the game. The ability to die and come back to life is invaluable sometimes. Don't rely on it however, as it's not a good idea to have to wait 5 minutes for it's passive to reset.

Spirit Visage

Spirit Visage's health and magic resist are both useful, along with the cooldown reduciton. The passive is also very useful. If you build one bloodthirster and a blade of the ruined king, you will end up with 40% lifesteal. This with the high magic resist and slight health bonus makes this one of my favorite items to build.

Maw of Malmortius

Maw of Malmortius is another item is also almost a core item. The high magic resist and shield passive almost warrant it's purchase by itself, and the damage bonus along with its damage passive combine to make a very powerful addition. If you started against an AP character, this item is a must, as it builds from hexdrinker.

Mercurial Scimitar

Mercurial Scimitar is an item that is good for damage and defense against an AP champ. It gives a good amount of damage while giving even more magic resist than the Maw. It has a moderately good passive as well. It is especially good against a crowd control heavy team. It is also good for last second chase or escape speed bursts.

Greater Mark of Attack Damage

Greater Mark of Attack Damage is an absolute must. With the slow start for attack damage with this build, taking something else would leave you hurting for attack damage. With it, it will help you farm minions and hopefully pick up the early kill.

Greater Quintessence of Attack Damage

Greater Quintessence of Attack Damage is again something that you have to take for the same reasons as the Mark of Attack Damage. This will give you around a total of around fifteen attack damage when to two runes combine. Along with your masteries, you should deal enough early game damage to get by until frozen mallet.

Greater Seal of Armor

Greater Seal of Armor will help to keep you alive in the early game, where physical damage generally reins supreme. The thirteen armor that you will start with you help immensely to deal with basic attacks or a AD skill based champ.

Greater Glyph of Scaling Magic Resist

Greater Glyph of Scaling Magic Resist is here for about the same reasons as the seals of armor. However, in the very early game, most characters will not deal a large amount of magic damage, at least until the scaling part of the glyph's will start to protect you. Be sure, however, to be extra careful around AP champs early game, as they will do slightly more damage in the first few levels.

Flash

Flash is one of the best summoner spells there is. With some creative use, you can escape or chase down an enemy with great success. The ability to go over walls is immensely helpful, and can save you or get you a kill when you would otherwise die or give up the gold from slaying an enemy.

ignite

Ignite is very helpful for getting an early kill or as a much better alternative to a turret dive. As long as you're in range, using it can secure a kill or get some good damage down. It is very important to know how much health your target has, how much damage your ignite does, and if your opponent has some sort of heal or health pots. All can factor into getting a kill or wasting an ignite.

Playing Kha'Zix during the laning phase as a Brusier AD is a little different then playing him as an assassin, but not by much. If you know how to play him, you can skip this section with the sole thought that you can trade a little better while taking less damage.

For all of you still here, I am going to assume that you don't really know how to play Kha'zix during the laning phase. Firstly, getting an early kill during this phase is key. It works out well that at level 3, or even 2, Kha'zix can do just that.
The first thing you're going to have to do is poke them down a little. Your Void Spike will suit your needs perfectly here. It has a good range and does a good amount of damage, along with 100% of your bonus AD. If your opponent steps away from his minions, punish them with some damage. It's a skill shot, so predicting their movements is key. If they stand close enough to their minion line, remember that it has a very small AOE effect around the hit target, so you can hit their minions and still do damage to them.
Once you have them on low HP, you're going to need to use Leap to get on top of them and burst them down. Make sure that you hit them with the leaps AOE for maximum effect. Once you're close enough, basic attack them to set off your Unseen Threat for the slow and extra damage. then you're going to Taste Their Fear and finish it with a Void Spike.
If you think that you can kill them, you can ignite and basic attack until your cooldowns are done. Once they are, use your abilities again and try to kill them. If don't think you can kill them, back off immediately. You don't want to take any more damage then necessary.
Either way you go, make sure to go into a bush or walk away from the enemies minions to reset your Unseen Threat. The slow from it can be the difference between a getting kill and losing it.
If you find that your opponent isn't taking much damage from your burst combo, then poke them down as far as you can and ask for a gank from you're jungler.
Throughout all of the laning phase,

make sure to farm minions

Fifteen or so melee minions or twenty ranged minions are worth a kill in gold, so they help immensely.

This is where playing Bruiser AD Kha'Zix really differs from playing him as an assassin. His AD is around 50 or so lower, depending on your chosen items, but his HP is much higher, as is his magic resist/armor. This leads to some interesting game play mechanics.
First and foremost, you can lead the charge into the teamfight if no true tank is there to do the job. I don't personally recommend it, as getting them to initiate normally works better.
This is the important part:

What to do during teamfights

Traditionally, Kha'Zix would jump in at the last minute to kill an enemy on low health, then jump out. However, with more HP and resistance to damage, a new way is opened up, especially if you combine a traditional bruiser with an assassin to get a potent champion.
During a teamfight, the first thing you want to do is decide which path to take. More assassin, or more Bruiser. It depends on a multitude of thing, foremost of which is team comp and how well they can do in a teamfight without you.
If you think that they can handle being without your for a few seconds without dying, then sit aside as an assassin would. When someone gets onto low health, jump into the enemy and go to town, just don't jump back out. If you find that your team is losing the fight, or it has gone on for a few seconds and is at a general stalemate, then jump into the front or back(preferably back) of the other team. This will let you both distract the other team as well as take the attention away from other players on your team, or deal large amount of damage yourself.
If you think that your team will begin to lose the fight badly as soon as it starts, play pure bruiser. Let the tank initiate, or do it yourself if there isn't one, then attack.
In both situations, it's important to focus the right characters. In most situations, you will focus their AD carry, then their AP carry, then whoever else you can while going after their tank last. Of course, some situations warrant different actions. You will have to decide whether to follow aforementioned order, or to target a different enemy champ.

Thank you so much for reading! If I left anything out, or you want me to change something, just put it in the discussion, or message me! I will try my best to keep this up to date and working as well as I can!