Welcome to my Kog'Maw guide, he is one of my favourite champions because he is just so fun to play! In this guide I will show you how to play him as an AD carry. Plz leave any and all opinions on my guide, I'm very open to constructive criticism.

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****************Pros*******************************************Cons
-Has extreme range***************************************-No gap closers
-Great high damage output*********************************-Little CC
-Safe farming in lane**************************************-Farm reliant
-Very fun and rewarding to play with**************************-Needs to be well protected
-Makes you feel like a MLG sniper

You don't have too good of a laning phase, as your base stats aren't great and you scale well into the late game. During levels 1-5 your focus is just to farm, don't be too aggressive as most other AD carrys will outmatch you early game.

Farming - I'm sure many of you know how to farm under tower, but I just want to go over it to make sure that you guys do this right. You will likely be pushed to the tower, so here are things you need to know.
Melee Creeps - Let them take 2 tower shots and then auto attack
Caster creeps - Let your support/laning partner auto attack them each once, then let the tower attack them once, then auto attack. (If your Lane Partner isnt in lane, you can do an auto attack followed by a Q to grab the last hits if necessary.)
Hopefully your able to grab most of the CS as it will help alot for Mid-Late game.

greater mark of desolationGreater mark of desolation
Provides Armor Penetration, which is better than flat attack damage needed to deal more damage to your opponent.
Alternative would be be flat AD, only take these if you have trouble last hitting minions.

Greater seal of resilience
Provides some need Armor, very useful for survival in lane, as it is where you struggle. There is really no alternative to this.

Greater glyph of shielding
Offers you scaling Magic Resist, as the enemy mid laners might often come bottom to gank at level 6, this might just be enough to help you survive.
Alternative to this would be Flat Magic Resist, I recommend taking this if your enemy jungler is AP(Amumu, Fiddles ETC.)

Greater quint of strength
Gives you additional AD, helps you last hit in lane, and deal more damage.
Alternative #1 Movement Speed quints, if you feel really comfortable without the attack damage quints, this could mean the deference when your chasing, or being chased.
Alternative #2 Flat Armor Penetration, again, if you feel comfortable without the flat AD, armor penetration will do more damage to enemy champions.
Alternative #3 Flat health, this is a good option if your up against a very aggressive lane(Graves, Missfortune, Leona ETC.)

As an AD carry, your almost always going to put atleast 21 points into offense. For the other 9 points, you can put it all in defense, all in utility, or a mixture of both.

21 Offense

Summoner's Wrath - If you choose to take Ignite, Exhaust or Ghost, take a point in this and take out butcher.
Brute Force - The more AD the better, if really have trouble last hitting, consider taking out points and put it into butcher.
Mental Force - You don't need ability power.
Butcher - The reason we have one point in this is because 4 points are required to move on, summoners wrath would be useless with heal, and you don't need ability power.
Alacrity - Gives you 4% attack speed, it might not seem like a lot, but every little bit counts.
Sorcery - Cooldown reduction wouldn't be useless, but the attack speed is just better.
Demolitionist - An extra 10 damage to tower will make minimal impact, I personally think that this is useless.
Weapon Expertise - An extra 10% Armor Penetration, how wonderful! This will increase your damage output, always take a point in this.
Deadliness - Attack damage per level, again free attack damage, the reason we take this over havoc is so that we can unlock lethality.
Arcane Knowledge - 10% Magic Penetration, well you could possibly take 4 points in sorcery and grab this for your ultimate, but that would be sacrificing either 5 points from the your trees. I do not recommend this.
Havoc - Increase your total damage output by 1.5%, it's not bad, but u value the points in vamparisism more for extra sustain during the laning phase.
Lethality - Extra 10% damage on critical hits, since you will be building phantom dancer and infinity edge, you will be criting often, having that damage boosted by 10% ain't bad at all.
Vampirism - Gives 3% very much needed lifesteal for lane, if you have soraka as your support and/or versing a very non-aggressive lane, you could possibly switch this for havoc for extra damage output, thought I don't recommend doing this.
Blast - Once again, you don't need ability power.
Sunder - 6 more Armor Penetration, the more the better. Always put 3 points in this.
Archmage - Well, for the last time, no need for AP!
Executioner - We didn't come all the way here to pass up on this, extra 6% damage when they're under 40% health, good for finishing off opponents.

Now you have the option of adding more points into offense, or put them in defense or utility. I would recommend either 9 in defense or utility, not a mixture of 2 or 3 of the trees.

9 in Defense

Summoner's Resolve - If you choose to use heal or cleanse, you'll sant to take this, otherwise put it in resistance.
Resistance - Your only putting one point in this because you will be up against an AD carry bot, so the 3 points in that would be much more useful spent.
Hardiness - Like I said above, the extra armor would be more useful than the magic resistance.
Tough Skin - Your really not gonna be tanking minions since your not jungling.
Durability - Health per level, as in the name, some extra durability throughout the game, this also gives you access to veteran scars.
Vigor - This is more useful for a jungler or top laner, the fact you'll be healed by either a support or your lifesteal, durability is better overall.
Veteran's Scars - 30 extra health, this might not seem like a lot, but it could make the difference between life and death.

I'm not going to go over the other 3 options, as veteran scars is the better choice.

9 in utility

Summoner's Insight - Reduces the cooldown of your flash by 15 seconds, I don't like this one myself, so it's really up to you, thought I preferr it over good hands and improved recall.
Good Hands - Reduces time spent dead by 10%, I'm not too big on this one either, it could make the difference in late game situations, but I think 3 points could be better spent elsewhere.
Expanded Mind - Gives you mana per level, I personally like this on kog'maw, it could give you an extra shot of your ult for a kill. I recommend taking 3 points in this.
Improved Recall - Reduces your recall timer by 1 second, sometimes it could make the difference in clutch situations.
Swiftness - increase your movement speed by 2%, I really like having this since kog'maw dosen't have any speed boosts or blinks, outrunning your opponent will be the best option.
Meditation - mana regen, it's nice to have on kog'maw, as along as you don't spam your E or R for no reason, you should be perfectly fine.
Scout - increases your ward vision, warding is generally your supports job, so you won't really benefit too much from this.
Runic Affinity - Increase your buff durations by 20%, this is pretty much the reason why you would be going for an utility tree. Kog'maw is a monster with red buff as you pretty much turn into Ashe with a huge range, also if you pick up a blue, you can spam your ult in lane and completely dominate it. And of course, never forget about baron.

Best spells

Flash - Defiantly neccassery on Kog'maw, being his only escape.

Heal - As kog'maw you have a very weak laning phase, so heal is a very good option to keep yourself alive during the laming phase.

Good spells

Exhaust - Good spell to help you win 1 on 1 engages, I would recommend this spell if the enemy team has someone like tryndamere who would just go straight for you pretty much in everyteam fight.

Cleanse - It's a lot more stronger late game compared to heal, take this if the enemy has a lot of CC or you have a team that isn't the best at protecting you.

Ignite - This spell is not great, but too bad either, if your planning to play very aggressive for whatever reason, take this.

Ghost - Not bad, but you don't have enough survalbility to make the extra distance count, so flash would be a better choice.

Teleport - Well, your not someone who would be attempting to back door often as you are needed in teamfights, though it could be useful if your being pushed out of lane often.

Bad spells

Clarity - You don't need this, once again, be wise with your mana.

Clairvoyance - It's not a bad spell, just not for you.

Smite - You'd be crazy to jungle kog'maw.

Promote - I don't think I need to explain this one.

Revive - Not a fan of this.

Surge - Never liked this spell, never will.

Garrison - I don't play dominion, but I'm pretty sure garrison isn't meant for ranged ADs.

Starting Items

This is probaly the best option for any champion, gives you nice movement speed and potion to sustain in lane.

Gives you extra AD, some health and lifesteal, Kog'maw has very weak laming phase, so the fact that your unable to get any potions is a problem. I advise to avoid this option.

If your up against a super agressive bot lane, you should consider this because it gives you the most sustain.

Recommended Items

- This is a good early game item as it gives some stats for a cheap price, I usually grab two of these.

- Gives you much need life steal to stay lane, since health potions will be less effective.

- Standard boots for an AD Carry.

- The reason I grab his first before infinitude edge is because your W gives you alot of extra damage. So grabbing attack speed would be more beneficial in this case.

- The best AD item in the grab, grab this after phantom dancer, provides you tons of damage and increases crit percentage.

- Now it's time to consider some defensive options, Guardian angel offers a some armor and magic resist, along with a revive with a 5 minute cooldown. Personally its my favorite defensive item.

- By this time your opponents will have decent amounts of armor, so take this if needed.

- Gives you attack damage and lifesteal. Good end game item.
Remeber the order of items can be changed. For example if your opponents docent have a tank, you can skip last whisper, or if they are never focisong you, skip Guardian angel.

Situational Items

- I personally hate building this item on my AD carries, but if your getting destroyed in lane, then could be a good option. You'll probaly want to skip your doran blades if going this route, otherwise you'll your main core items will be delayed for way too long.

- Well if the enemy team decides not to build armor at all, you can build this instead of last whisper.

- I really dont think you'll ever need this item because your W also deals max health damage.

- Are you getting fed? If so you might wanna grab this(recommend for normal games only).

- Are getting raped?

- Does your enemy team have alot of CC?

- Is your enemy caster the problem? If so replace guardians angel with this.

- Does your team need more CC? If so replace guardians angel with this.

- Another item for casters, I haven't expiremented much with this, so I would recoomend banshees veil for now.

- Are you up against soraka, Mundo? I've seen some use of this to counter healers/high health regenerators, but the range on his thing is dosen't work well with kog'maw.

Good suppOrts for kog'maw
Soraka - Gives you free health and mana, along with her passive, she does a good job of keeping you in lane.
Janna - She only has a shield, but provides lots of CC to keep you safe.
Sona - She also does a good job of healing and provides some defensive stats for you.