Gj ;)

Your rune set and items are focused on Ability Power, but your skill set does not. If you are really going to go AP, maxing Vorpal Spikes and Feral Scream is bset. Take Feast at 6,11,and 16. It scaled well with ability power, and also makes it true damage.

Your build very much confuses me...

First off, you have 6 points into feral scream and only 2 in your ult. You don't take feral scream until level 8? WTF?

You level vorpal spikes first but you build no AS?

You build tons of AP but ignore the CDR and AK in the offense tree?

Why would you ever build a PD on Cho?

Why wouldn't you run flash on Cho (max range rupture lands > flash > feral scream > nomnomnomnom > profit.

Build needs HEAVY adjustment to be anywhere near ideal.

You should really level Feral Scream first. Then invest into some AS before investing too much into vorpal.

Personally, I like a stinger on my Cho. It's cheap but effective and gives CDR for more nom stacking.

That wall of text... BBcoding makes a guide better to read, JhoiJhoi's guide could help you.
Also, 3+4+5 Vorpal Spikes doesn't work, take another look at your level-ups.

I admire your effort and dedication, but I think you should add more coding and colour to make the text be more attractive to read. Otherwise, +1. (Refer to jhoijhoi's how to make a guide to learn how to code)