Hello guys!This is my first build here on mobafire and I hope that you all will enjoy it! :)
The reason for the title ''ChoBall'SnowGath'' was by meaning Snowball Cho'gath because as the game progreses,he has more and more health,armor and magic resist. :P

PROS

-VERY durable late-game
-Good armor and magic resist
-Can still last hit due to his passive

CONS

-Not much damage from his spells
-Mana problems early game
-Kinda slow-moving

For my runes,I chose:

Greater Mark of Health for the health,
Greater Seal Of Defense for the armor/lvl,
Greater Glyph of Scaling Magic Resist for the MR/lvl.
Greater Quintessence Of Vigor for the HP/per5

For my masteries I go 21 in Defense taking all the armor,magic resist and health masteries and 9 in Utility for the increased mana/health regen and extra gold/10 seconds.

GOOD SUMMONER SPELLS
:Teleport:I use teleport because it allows me early game lane presence and for mid/late game it allows me to go and take out these minion blobs that start gathering in the lanes to either a)get my feast stacks up or b)regen some health due to my passive by last hitting.Set your masteries accordingly.

:Flash:I like to use flash because Cho'gath isn't the fasted champion in the league and when you are being chased it helps to either flash into a bush or over a wall to save your stacks of and/or save your stacks.Set your masteries accordingly.

:Ignite:Ignite is good but you don't want to be stealing kills from your teammates since you are the tank.I suppose it serves a role in first blood but it doesn't scale very well into late game.Set your masteries accordingly.

Exhaust:I also use exhaust if no other teammates didn't take it to help when killing enemies or for getting first blood with ignite.Set your masteries accordingly.

:Ghost:If you prefer this over flash it does the same function except you can't jump over walls.Still viable choice.Set your masteries accordingly.

:Cleanse:Cleanse is also a viable choice because Cho`gath is VERY affected by CC and that will help him escape early game and also late game.Set your masteries accordingly.

BAD SUMMONER SPELLS
Clarity:I don't like clarity because you don't need it as much on Cho'gath even if he almost always is mana starved because I always get blue buff when nobody takes it or needs it.Plus it fills up a spot in your summoner spells.

:Clairvoyance:This is for support characters.

:Heal:Heal isn`t good in my opinion because people use this to heal while/after overextending and it will make them overextend again and again.

:Revive:No.

:Smite:Are we a jungler?No.It could help but we don`t need it.

:Fortify:Same with clairvoyance,it is more suited for a support.

:Rally:Is it even worth it?

His passive,
:Whenever Cho'gath kills a unit,he gain 33-66(+2.0 each level)health and 3.25-7.50(+0.25 each level)mana.

This passive is one of the best laning passive IMO because it lets you stay in lane longer and even if you get harrassed you can regen your health.

His ''Q'' skill,
:Ruptures the ground at target location.After a short delay,enemies are launched into the air for 1 second,dealt 80/135/190/245/305(+100% of ability power)magic damage and have their movement speed slowed by 60% for 3 seconds.

This is good to disable/slow enemies for a short time.But remember to have that 0.75 second delay in check so that you dont miss.

His ''W'' skill,
:Cho'gath screams in a cone in front of him,silencing enemies for 2/2.25/2.5/3 seconds and dealing 75/125/175/225/275(+70% of ability power)magic damage.

This skill is good to harrass if the enemy has to come close to last hit(melee champion),and is better if your against an AP caster,just back up,let him come and then get close and scream.

His ''E'' skill,
:Toggle:Cho'gath's physical attack launch spikes which deal 20/35/50/65/80(+30% of ability power)magic damage in a line in front of him.

This ability is good at harrassing the enemy melee when you autoattack minions.Be careful though,because if it hits and enemy champion at his turret,you will receive turret aggro.

His ''R'' skill,
:Devours and enemy unit dealing 300/475/650 true damage (1000 to minions)that ingores armor and magic resist.If the target is killed,Cho'gath grows,gaining extra health (max 6 stacks).Cho'gath loses half his stacks(rounded up)upon death.

For my starter items I take and a then head to either top lane or bottom lane.On my first trip back I buy ,but if I don't have enough,i'll take and another and then when I have enough,i'll buy the .On my third/fourth trip back to base I like to get my and a or straight a .Then I get my for the flat health,armor and attack speed reduction upon activate.If you find the better,take it for the increasing health and at 20 stacks for reduced damage done to you by 15%.By this time I have bought my or if you prefer, you can take the first and then get the ,and lastly,for my survival item I like the for the magic resist because you already have a lot of armor.

For my skill sequence I like to max to slow/stun the enemy and allow my teammate to gank/kill the enemy for either first blood or just a kill.Then I like to take 1 point in for the better farming.At levels 6,11 and 16 I put a point in and I put a point in early for the silence and then max last.

So this was it guys please vote and comment for this build to go up and hopefuly be the most used. :) Thanks for your support!