DISCLAIMER: A lot of people play AP and Hybrid Kog'Maw. Whatever floats their boat; AS/AD Kog'Maw is far superior. It's like playing AP Teemo or AD Twisted Fate, fun, but just not as good.

The whole idea of this build is to have a heavy farm, don't lose your lane and when the time comes, win team fights. Don't worry about the ganking stage of the game (happens hwen junglers start popping out)

Kog'Maw is the highest damage dealing ranged carry in the game. His issues include low survivability and zero escape ability. Through my item build and ***** play-style (let's call it that) you will be able to wreck entire teams. I've had two Quadra kills in a single game and a delayed Pentakill in a ranked. Trust me when I say that Kog'Maw is one of the most capable champions for completely turning the tide of a game.

There is one true key to playing Kog'Maw and winning: Never give up. If your team is losing, reassure them that you are Kog'Maw and you will carry them out of ELO hell! Stick with the plan and you will have success.

First and foremost. Do not gank. It's not worth it for Kog'Maw; hes slow, hes squishy, he lacks any type of escape or survivability.

Laning Phase Your job is to last hit and harass. Did I mention go bottom? Bottom lane being baby sat is your best case scenario; you can take mid but never take top. What you need to be doing is just straight farming. If you're bottom lane and Ashe moves forward to use Volley, drop your Void Oooze and immediately press W. Lay it onto her. If you aren't 100% sure you're going to kill her then turn the hell around! This is your entire strategy. Don't worry about kills if your creep count is going up. Just lower her health enough so that your jungler can be ready for some successful ganks! Try to save your Ghost/Flash for offense when your jungler comes to lane to gank. Ghost for closing in so you can help and Flash for either getting that last hit or escaping!
TL,DR Farm! Wait for your enemy to get too aggressive and lay out some E & W. Back up early because a lucky stun or knock up and you are out of commission. You're more likely to die than get a kill, trust me.

Did you get middle lane? It's ok. Just play like a huge *****. Stay behind creeps and farm. Use your W to harass periodically, but always back off. Let your jungler and enemy create kills for you. People get bored and get aggressive and with your huge slow (E) and insane range (W) you will be able to harass and pick off and enemy with Living Artillery, leaving them wondering what the hell happened. HUGE TIP: Do NOT pass your own creep wave chasing. If you get their creeps onto you then you are harassing too hard. Kog'Maw is WAY too squishy to be eating any type of damage. If their jungler pops out, it's 100% death. It doesn't matter if flash is up, you are dead. Just play like a huge ***** and farm, harass. Your time will come when team fights come.

End of Laning Phase When all **** goes to hell it's really important for you to continue farming safely. Farm your jungle (not theirs!) and farm any lane thats over pushed. Do NOT push out. Again, Kog'Maw is really bad at 1v1 against any champions with closing power. Don't risk it! Just stick with the plan. Once you pick up your Trinity Force it's time to start hanging REAL far back and stick with your team, far back! Once a team fight begins, make your way towards it. Pop your W and start laying out Living Artillery whenever necessary. Make sure to not overuse Living Artillery! Once the team fight starts winding down you should be using Living Artillery to finish off anyone who survived your slaughter.

OK, TEAM FIGHT OVER. Did you survive? You did something wrong. You need to absolutely make sure that you are far out enough and positioned in a way so that your enemy MUST go through teammates to get to you. Imagine your Fiddlesticks. If the enemy sees a Fiddlesticks then they are prepared. MAKE SURE THEY ARE NOT PREPARED FOR THE KOG'MAW!

Item build is extremely specific and there is no wiggle room. I dislike not having an open build to adjustments but this build is too specific. The whole idea is that sooner or later you're going to become this beast. If you are sticking in items like Banshees or Thornmail then you are significantly slowing down your progress towards being a destroyer.

Start out with Doran's Blade, typical. Try to grab Phage and Boots in one shop. If not than just grab your boots and hopefully Ruby Crystal. Finish your Phage ASAP. Pick up Zeal next but then proceed to build Phantom Dancer. Finish of Trinity Force. At this point you should be on God Mode. If this isn't true then somethings wrong. If this isn't the case then you should probably pick up Vamparic Scepter right away just for some sustain. Finish off your Infinity Edge then build your Blood Razor. Pick up Blood Razor if the games still happening. I still haven't finished a Blood Thirster going this build... but if you can? Why not.

OMG U AINT RUSH BLOOD RAZOR U BAD!Untrue. I am the first to admit that Blood Razor is must have on Kog'Maw but trust me when I say that Phantom Dancer and Trinity are way more important. You need that movement speed to give you the maneuverability and speed to be safe. You could pick up Blood Razor after Trinity Force but your attack speed is already so high and so is your critical strike. Infinity Edge adds that extra oomph so you can begin playing with your face once you obtain it.

Reds: Armor Penetration and no exceptions here.
Yellows: I like Mp/5 by level. Again stay away with Attack Speed, you'll have enough of this. You could go with Dodge but again... if you're taking damage with Kog'Maw you are doing something wrong.
Blue: Go with what you want. I stick with Magic Resist/Lvl because it's a solid choice and helps with harassment. CDR is a solid stat but I don't struggle with waiting on cooldowns ever.
Quintessence: Either go with Armor Pen or Movement speed. With my build you will be fast as hell. It doesn't hurt to be a little faster.

Masteries are pretty straight forward. You can swap it up and go 9/0/21 but I don't. Kog'Maw is here to destroy worlds. I hate building offensive in masteries but defensive serves no purpose. If you get caught you are going to die (probably). I did not take Alacrity because with my build you will not be short any attack speed. One point in Utility Mastery is a huge bonus because you will be killing a lot of people taking buffs and you should be stealing any red you can.

Pros:

Heavy damage
Ridiculous Range
Ability to win team fights

Cons:

Low hp
No escape, even with flash
No CC outside of a slow
No survivability

This list of Cons is daunting. Believe me when I say that Kog'Maw will win team fights.

Don't Gank

Farm like a boss

Never cross past your enemy teams creeps for anything other than a team fight

Don't go into their jungle

Don't roam through the river

Grab red buff often

REALLY IMPORTANT: Stay back before a team fight begins, like a Fiddlesticks. Let the enemy teams Crowd Control be on cooldown, once it is you will be able to slurp up anyone who is sadly enough in your range.

Don't forget about Void Oooze. This is really good for slowing an enemy that's darting towards. Once you have Trinity/Phantom Dancer you can outrun a Singed (without Ghost) by laying out your E Void Oooze.

Stick to the plan! Play like a huge *****. You should NOT be too aggressive. When you stick back you can easily kill people with your W and not have to worry about them ever getting near.

In this area I'll repost and try to answer any questions. This is my very own build so I'm open to anything anyone has to say.