Hi this is my first guide so foregive me if i'm not enough explanatory or miss something.
in this guide i want to have a closer look to cho' gath and share with you something i think it's a good build.
So start reading.

This is cho's passive.It's a good skill to lane as long as possible( it restores heal and mana whenever you kill a unit), and keep you farming.

This is cho main ability, this allows you to launch enemies in air and slow them, making it a great ability either for chasing or to flee.

This is absolutely my favourite skill; an AoE silence that can shut down an entire team if well setted(it also deal quite good damege ideal for farming and harrassing).

Not the strongest ability at all but it's very useful: it deals damege at all enemies in front of you, even champions, so it can be used to farm and harrass at the same time, but you'll need a good positioning.

Cho' gath's ulti, this ability is amazing it provides you quite a lot of healt to make you even more tanky and deals 650 true damege, ideal to scare annoying carries or last hit an harrassed champion.

as all champions also cho' gath has his pro and cons:i'll give you some.

PRO

very durable during laning phase.

deal an enormous damage with FEAST

YOU'LL BECOME F****NG BIG WITH 6 STACKS

you're the terror of the void

nice nuking combo

eats enemies

CONS

needs smart play

melee

if you go full tank, you waste his AP strenght

rupture needs to be mastered

you'll become predictable late game

I took standard defense masteries because this is a tank/AP offtank guide, so you need defense, i choose mercanary over honor guard first of all because mercenary works great early game, so when you lack a bit, second because the damage reduction of honor guard makes me laugh(forgive me if i'm wrong); however, if you prefer to take honor guard it'll be also fine.
wit the 9 points left, you can upgrade either utility(mana) or offense(CDR and AP).
I decided to boost utility because they provide more mana and mana regen, that's always needed on cho'gath.
However if u are wise enough to not fooling spam your abilities, i suggest you to go for offense and take mental force and sorcery, to have feast more available in mid/late game; then pick arcane knowledge to boost your abilities.(those masteries can go better if you are going to use the AP build).

for runes i take magic penetration marks, to make rupture hit harder early game;
then go for armor per level seals, flat magic resist gliphs and gold per sec quint.
(gold is always needed, even if u aren't a support).

I suggest you to take teleport as a standard spell because you should go soloing top as often as you can, and this will help you to don't waste time and keep you farming.
however, if you can stay in lane without taking serious damege and own your opponent
it could be fine to pick another spell.


Flash is a must since you haven't a very effective escape mechanism; yes you have rupture, but is not so effective as it looks like.

VIABLE CHOICES

other viable choices are:

exhaust:Always help either for chasing/killing or escaping, it can shut off a carry, so it's very good but i'm not so scary about damege, you have a nice burst and nice defensive stats, so you can tank well enough to not take it;

heal: What i can say? more survivability, it can help, but in a gank your healt will be burst down, so i prefer flash;

clarity: I find it nice because at early game you'll be always mana starved, but with meditation as mastery and a wise use of your spell, you'll find yourself quite comfortsble even less this(you can also kill creeps and let your carnivore give you back some mana).
however, i suggest you to take if u go for a CDR runes and masteries or if u are improving;

ignite: Would you like other true damege? here you are!
if u want to burst down your enemies, you can deal 650+ 410 TRUE dameges at level 18.
if u like see them flee, take it.

cleanse: Can be useful if you are facing an heavy CC team, but i suggest you to take quicksilver sash if you are facing heavy CC.

carnivore: I think this is self explanatory, use it to heal and recover mana in order to back fewer and let your jumgler gank.

rupture: Most people say this is your main skill, but i don't think is exactly true: you must know when use it and you need to master, but i think that feral scream is more important.
Yes, this ability will save your *** so many times that you wouldn't count them, but it's better if used as a chase skill.I'm not saying you won't use it to escape, but i think feral scream is more useful.

feral scream: This is an amazing AoE silence that can hit an entire team, dealing also damege.
Use it in combo with rupture to harrass and kill minion waves, the enemy champion will be slowed and silenced and he'll fall back letting you farm.
when you reach a good damege otput, you'll be able to kill caster creeps by using feral scream and rupture: fast 60 gold.

not a lot to say: Easier to kill creeps and a good harrass item.
I prefer to max it last because it sinergise well with wit's end, that's the second-last item to build.

feast:You can

gnomgnomgnom

your oppents and deal 650 true damege, so you'll see the healt bar falling down, and so your oppent will do.
Remember that you can combo with rupture and feral scream, to deal "tons of damages" to your oppents and see them recalling; if they don't recall, be happy, harrass more untill they drop at about 700/800 healt and repeat the combo:easy kill for you.
ATTENTION: Don't waste mana harrassing people like dr.mundo, i played it and i got 6000 hp, that means that feast is 1/10 of his life,and he will simply laugh in your face and hit you with masochism and burning agony.
However don't be scared to use your combo's, they can burst quite a lot of healt and harrass enemies.

Here you are an example of cho's burst damage(all rights to the owner) Play Video

REMEMBER THAT YOU ARE TANKY AND YOUR BEST FRIENDS ARE:








These 3 items provide you a lot of survivability(to stack feast), that is always needed, and will make your lane easier to sustain.
If you find the build so much expensive, try to start with boots and 2 mana pot. (you shouldn't need healt pot because of your passive; if you aren't having a good time, buy healt pot instead).
Continue laning until you reach 2400(more or less)gold, to buy mercury's tread and catalist.
Once you get catalist i suggest you to don't back at least once you can buy negatron cloack and chain vest, so 1440gold.(i think that you shouldn't back untill you reach level 16, but you should know when it's time to back).
Stay in lane as long as you can to maximize catalyst the protectorcatalyst's effectiveness and take a level and gold advantage on your enemy.
Well, now you should have enough armor and magic resist to tank a lot of damege, and you won't to go back untill you can buy either banshee's and sunfire cape.
Now it's time to build damage, and and
is what we're searching for, they provide either damage and armor, perfect for a tank.
Once you have bought this items, you'll need extra armor and CDR(frozen heart) or movement speed and magic resist(force of nature); you'll choose force of nature if you are facing more casters/meges, you'll pick frozen heart facing more AD/fighters.

I'm giving you some guidelines for gameplay either becuase you need to find your gamestyle and because i can't foresee all players and champions you'll face.
HERE YOU ARE SOME TIPS:

Remember that you are the tank and unless it's useless you should die to save your carries.

Don't forget that you can deal burst damage and scare people with your AoE CC and your FEAST.

If you see you are doomed, don't be scared to burst enemies and try to kill someone.

You are a tank, but it doesn't means that you can't deal damage or kill opponents.

If you miss some healt remember that killing creeps heals you(land a rupture and a feral scream at max level on wraiths will heal you a lot)

Try to play smart, so don't tower dive an half healt champion when you're at level 6 with feast on CD

When you push a tower could be wise to turn off yourvorpal spikes, because they'll hit everyone in front of you, even a champion and you'll be hit by the tower.

Seeing this video could help you having an idea of your laning phase. Play Video

(i don't own this video and all rights reserved to the owner)
See how rupture eats mana and it's a big waste if not landed, so master it.
See that you also need farming, this is why soloing top is simply great.
Remember that feast is like smite, so use it to steal red, blue or dragon.

So now you can ask:
why don't take a deathcap instead of wit's end?
Deathcap is surely a good item, but costs 1000gold more than wit's end.
It will also boost your feast, but remember that feast has a very short range, so you can easily auto attack with wit's end few times and deal also a lot of damages, considering also atma's impaler.
However, if you want take it, i suggest you to take a different build, like this below:



This build will allow you to deal very hig dameges and still be tanky, so if you like it,try.

i suggest you to change a bit your build if you are facing heavy ao/ad team.


AGAINST AD





Start with shield, then once you get enough gold for ninja tabi, go base and buy.
continue laning till you get 2000gold to buy either chain vest and giant's belt.
after that there'll be so much teamfights that you'll need to go base quite often, so buy when you can.



AGAINST AP TEAM:


catalyst the protector


Against an AP team try to harras once you see your opponent has cast his nuke spell(ex. land a feral scream/rupture combo once you see galio has casted his smite with his gust).
Try also to stay out of your opponent's range while farming and try to land some spikes to harrass even well.

Thank you to read this guide i hope you find it fun and useful.
special thanks to jhoijhoi and her guide for helping me making this.
Gl & Hf