Yes I know he is squishy in the Beginning of the game. But his damage output in mid/late game is really high. For smart players he is your best choice. As Kog'maw has BONUS magic damage with Bio-Arcane barrage. making him a force to be wreaking with.

I pick All attack speed. Why you ask? Because He is attack speed dependent. starting with 1.0 or higher in attack speed is really good.You could go with Armor pen. But this is my recommendation.

This is Very Important. You start with Ooze to slow enemy champions down. To help you or your teams to get that first blood.Then when you level up. Get that BIO-ARCANE BARRAGE to increase your attack range and Bonus magic damage for 2% of the of target max hp (PER HIT). This is where you should start getting kills. Pick off weaker champions(or lower hp champions) Rememering to slow them down with Ooze and then Turn On your BIO-ARCANE BARRAGE for damaging them. your range should be almost 200 with your basic attacks.Then When you Level up to level 3 put skill point into Bio-Arcane Barrage. To increase your added range to 160 and bonus magic damage for 3% of targets max hp(per hit).

This is the stage of your core of your skills. starting with your Caustic Spittle for the passive increase of attack speed of 10% this is very handy with your Bio-Arcane Barrage. Followed by a level in Bio-arcane Barrage. For a total added range 190 and magic damage for 4% of the target's max hp(per hit) By this time you should have Madred's Bloodrazor which does 4% of target's hp as magic damage(per hit) giving you a total of 8% of the targets max hp Per hit. At level 6 you get LIVING ARTILLERY, this is a very handy tool to have. I primary use this skill for checking bushes as it reveals enemy champions in bushes.Or final hitting on enemy champions that are running away. as this skill has a very low cool down. Of 2 seconds but if used within 6 seconds adds additional 40mp cost per usage stacking up to 5 times. so use wisely.

Continuing to level up bio-arcane barrage for the the added range of 250 and magic damage of 6% of target's max hp (per hit)(+1% per 100 targets abilty power) This skill is the bread and butter of My kog'maw. with Madred's Bloodrazor you total magic damage per hit is 10% of targets max hp per hit. plus 1% per 100 of targets AP. usually i don't make it to level 15 the enemy team surrenders b/c they say i'm taking them out to fast and getting aces left and right. and that im Pro with Kog'maw. Even on Ranked matches.

Getting Berzerker Greaves is very important as it gives you 25 to your attack speed and 2 to your movement speed. As i said before attack speed is very important with this build.

Zeal Is the next item on the list as it attack speed, movement speed, and crit rate.

Madred's bloodrazor is the Bread and butter of the items it is the most important item to get.

Phantom dancer, upgrading from zeal this is a very useful item to have for the attack speed giving you 55 to attack speed, 30 to critical chance and 15 to movement speed.

Infinity edge is for damage and crit chance. this is also a back up so that enemy champions cant stop ur damage output b/c ur main damage is magic damage while this secures your damage as Attack damage they would have to get thornmail and force of nature to stop you, by that time they cant do damage b/c they got the armor instead. while Critical will still hit them hard.

Everything else is Up to you but this is the core of my Items.

This is important to get attack speed and critical damage on offence. while on Utilities getting mana regeneration and movement speed. This can Be changed to fit your play style. But my build i recommend.