Cho'Gath is a bit weak before level 6, relative to other top-laners. The goal before level 6 is mainly not to die, and to have mana so that you can Q and/or E. You might need your buttons to help your own jungler, or you might need them to escape. There is nothing more sad than a Cho'Gath with no mana, and levels 1-5 is when Cho'Gath most feels it.

Another way to frame this decision is that Cho'Gath uses Q to farm/poke safely. It is better to have 4+ more uses of Q before you run out of mana, rather than having each Q do marginally more damage. Starting with 250 extra mana can get you more farm when under pressure early.

Cho'Gath will get to level 6 before you know it. When he does, you want to be at 30% CDR if you can so that you can begin stacking health from your R. It isn't reasonable to use R on minions if you don't; but doing so nets a huge amount of extra health "for free" and is important to Cho'Gath's ability to slowly take over the game. Between lots of CDR and Ultimate Hunter, Cho'Gath will not struggle to have his ultimate ready to eat an enemy champion.

Always get your CDR right away. Only get that and boots. Once you have it, decide what items you want to complete first.

Chogath's midgame build should look like one of the following:

SURVIVING VS PHYSICAL
Mercury's Treads
Stinger
Fiendish Codex
Frozen Heart
Dead Man's Plate

SURVIVING VS MAGICAL
Mercury's Treads
Stinger
Banshee's Veil
Glacial Shroud
Negatron Cloak

GOING AGGRO VS PHYSICAL
Mercury's Treads
Nashtor's Tooth
Glacial Shroud
Dead Man's Plate

GOING AGGRO VS MAGICAL
Mercury's Treads
Nashtor's Tooth
Righteous Glory
Negatron Cloak

Exactly what order you build everything is fluid; there is no set path after getting your CDR. Just stick to the full item list and build toward whatever you need -- defense vs physical, defense vs magical, more offense, or better pursuit. Remember that the enemy in your lane may not be the one you need to worry about. Build also to deal with the enemy jungler and to shrug off the most fed enemy champion's offense.

You are going for 170 armor and 140 MR on Cho'Gath because he has infinite health scaling and armor/MR makes all that health more valuable. But there is more to this build that just being a ridiculously hard to kill tank. The secret is Dead Man's Plate, which gives you +60 move speed as you come barreling in on enemy champions. This allows you to engage with E, rather than Q. It also makes the enemy's retreat path a lot easier to predict, since if they dodge your Q they will get hit by your auto-attack. Cho'Gath's E-empowered auto-attacks have a strong slow on them. After Q's knock-up, Q also applies a slow. Nothing gets away from Cho'Gath. You just have to build him so that you can rush in like that without being nuked off the map. There reaches a point with Cho'Gath where plays that would be full on "inting" instead become Cho'Gath casually 1v5'ing the enemy team.

Cho'Gath's game is simple; get as many R stacks as you can, as fast as you can. Get the 6 minion stacks. Get dragon stacks. Get Rift Gerald. Eat Baron Nashtor. The more you eat, the stronger you are. It's not just your ultimate. Your E begins to reach the point where it will shred the entire enemy team -- you have Hail of Blades and Nashtor's Tooth, so you will triple-proc the empowered E and do a giant chunk of percentage max health damage that is ramped by 15% thanks to Abyssal Mask. Nobody survives for long vs Cho'Gath.

The enemy team will want to do two things to stop you from becoming this strong:

First, they will try to end the game before you get out of control. So Cho'Gath goes well into team compositions that are otherwise strong early, such as ones with Talon mid. If your team takes "rushing a win" off the table, Cho'Gath will carry them with ease if the game goes long.

Second, they will try to focus you down. They will gank you aggressively in lane, go for picks when you split push, and go for you first in team fights even though you are the tank to keep you from eating someone. Cho'Gath, while he lacks any sort of jump or dash, can quickly get into 1v2 mode. Don't be afraid to just full up murder somebody when you see the 1v2 coming. Eat someone at you more than break even there. Sometimes you'll kill them both. Your CDR will help you a ton. Q and E are both excellent 1v2 tools, and they can be used to escape if you can't fight.

Being bloody terrible with Q is why most people think Cho'Gath is not absolutely terrifying to face. But this power, when well placed and well timed, is reasonably easy to land and effective even when it misses.

First, the delay between the visual animation of Q and when it hits is small. If you wait for an opponent to auto-attack, use a button of their own, or just walk toward them so that the ONLY way they can go to avoid you is away from you... you'll often land the Q. When enemy champions get in your face, it gets even easier. Put the Q under them, with the circle touching your feet. Even if they move to dodge it, you are auto-attacking them the entire time (applying a strong slow) and will have your Q up quickly thanks to having 40% (or early; 30%) CDR.

I like to hit E first, then Q afterward. They have to guess when the Q will come. Sitting on Q and not using it makes opponents very nervous. They count on you being a bad Cho'Gath and tossing out the Q in a vain effort to engage. The moment you miss they dive you, try to short-trade, then get out before Q is back up. Don't just walk into that predictably. You can definitely poke with Q, but Cho'Gath wants the food to run. Let them run away and just out-farm them. Eat a minion in front of them once ahead, to bait them in (because you don't need R to kill; you just chain slows and auto them down). As long as you stack R, it doesn't matter what the food is.

Let's start with what mage Cho'Gath is good at doing; one-shotting someone who cannot survive his combo. The combo is typically Protobelt or flash (out of the brush to get close enough and surprise the target), W to silence the target so it can't get away from the rest of the combo, Q to keep them near enough to auto-attack, then 1-3 empowered auto-attacks before eating the target with R. If Cho'Gath is initially successful and can get AP with the kill gold, this becomes an increasingly powerful combo. If the combo fails? Well... gg. Mage Cho'Gath doesn't have a way to power up. He is reserving his R use to get kills, so he doesn't have enough stacks already to switch into a build like this one. And he's bought AP instead of armor/MR, so he's very easy to kill when ganged up on. This makes him many times weaker in a team fight than tank Cho'Gath.

There is also the issue of the enemy dealing with your brush hiding spots or building to survive mage Cho'Gath's combo. Maokai and Teemo both frustrate mage Cho'Gath especially, since they have nasty ways to check the brush or trap it. But any champion can toss a skill shot into the brush; runes like Summon Aerie or Arcane Comet give away that you are there. Health + MR items kind of shut down the combo as more than a poking tool that burns almost all Cho'Gath's resources then leaves him vulnerable.

The advantage of tank Cho'Gath is that he gets to the point where he beats other top laners 1v1. There is almost nothing the opponent can do unless they are on the right champion AND are a far better LoL player than you are. Even then, the best they can really hope to do is suppress you long enough that the game ends before they lose almost all ability to fight you. He is the best hyper-carry in the game. He gets infinite health, and both his E and R scale for infinite damage. All three of these traits scale without any items all. So the best build for him is to defend that health and make sure that offense reaches a target (with the mana and CDR to have access to it). You end up with an anti-cc + armor/MR build, with Hail of Blades to insta-proc E three times into the enemy team.

When you are against a team that is all-physical or all-magical, you have to punish it. But such a thing can be difficult for tanks to do, since armor/MR buys do eventually get diminishing returns as far as value. I have included the alternate items in the item/build section, to best punish teams that don't respect the need for a physical/magical balance in their composition. Notice that I suggest for you switch out armor or MR for extra team-fight oriented offense.

Titanic Hydra is an item that scales infinitely on Cho'Gath. You aren't buying it because it gives you health; Cho'Gath already has tons of health. You are buying it because it turns your health into damage. This is an item that you can opt to sub into the normal build -- either in place of Dead Man's Plate if you don't need chase speed, or in place of Banshee's Veil if you don't need the anti-ability shell. It is a bit slower on CDR to do... but you can actually replace Nashtor's Tooth with it. There is enough CDR in all versions of the build to do without Nashtor's Tooth.

In some games, you'll find that you are a split-pusher more often that the vanguard initiator for team fights. This is where attack speed matters most to Cho'Gath, and you will get Wit's End as one of your MR items to augment Nashtor's Tooth (or sometimes as your only AS item; if you built Titanic Hydra in place of Nashtor's Tooth). I suggest building Wit's End in place of Abyssal Mask if towers are truly your main target, though in my own games I tend to replace Banshee's Veil as a sort of compromise. Be aware that you can replace either item.

If you haven't checked out my ADC/tank Yuumi support build, you should! It can be played top into every match-up without much issue, except maybe into an Illaoi that like to hard-push when you have an AFK jungler than won't help you punish it. Vote on it too, after trying it a couple of times. You will be surprised how strong Yuumi can be on the ground.

This Cho'Gath build is not a KDA stacking beast early; I don't like glass cannon one-trick builds. But even in 20 minute games, the enemy will begin to fear Cho'Gath and avoid him. You do get into the position where, if you don't win, you start to rack up a serious KDA. I've gotten over 60 kills with tank Cho'Gath before, and I've also killed the entire enemy team when they came to 1v5 me while I was split-pushing. I'm not the best CHo'Gath player ever; it's just the build and the tactics. You can literally carry games on 400+ ping with this. All he does is wade in and kill everyone. Good luck on the Rift.