I guess you're right. I did kind of get a little lazy halfway through it to be honest. Also I usually don't bother with runes and stuff so I didn't really know what to put there. I'll trying working on it more later. I wasn't planning on making a full on guide because that seems like a lot of time and effort, I mean I did take about 4 or 5 days to make this :/. I just kind of wanted to put this build up because it works really well. But anyway thanks for the help.

That's a pretty valid point.

So yeah, Starting with the runes. Scaling ap quints only become as good as flat ap when you hit level 12 or so. by which time the bonus will be pretty minor. Flat ap quints will give you a much stronger start upto level 12 ( which is a pretty long time).
Swap the scaling ap marks for magic pen marks. They've proven time and time again to be stronger than any ap runes. Change the Glyph of Magic Penetration into either ap ( scalings ok for glyphs, since they beat flat at lvl 6) or magic resist. Seal of Armor are pretty damn strong + mages still auto attack, so the armor isn't a waste in midlane.

Tomorrow's spelt incorrectly in the title :/

your core build should consist only of items you build every game or 90% of games and not optional items (like 2 sets of boots). Anything which is situational, isn't core. While Frozen Heart is a good armour choice, you should include items for Magic resist should the enemy be dealing mainly ap damage (maybe Spirit Visage or something. Otherwise cho will be especially squishy against their fed mage.

Take Veteran's Scars in masteries as the minor boost in health can save you in early confrontations. that aside your masteries are fine.

In terms of the actual guide, its pretty short and doesn't explain any nuances of to use Cho'Gath. like, what are good choke points on the map to use rupture in, what matchups does cho excel/struggle in etc..

Not trying to be malicious or anything, but this guide needs work.

What's bad about it? Just saying it's bad doesn't help anyone...

God bless duck punchers everywhere

Everything is so bad it makes me want to punch a duckling.