runes to start. AP runes with magic resist but no armor runes? i doubt you will need 3 types of AP runes but without any armor. your'e just setting yourself up for failure. what if the enemy is a zed, kha'zix, or even a sion(yes it is a thing)? you have some decent items but the CD boots and archangels or the trinity force. I could forgive all that but you dont really go in depth with anything. the guide is just too short.
the BBcodes not too good either but hey, im not very good at it either.

Nether Rifted even so much as a Null of Void so lets not Force this issue :)

You obviously dont rift

I honestly made this guide as one for my friend who is quite new and loves AP mid carries. Thanks for your...erhem...constructive...criticism, and I'll consider all of it. But this guide wasn't to be anything serious for ranked play and all the serious stuff, simply a muck around quick downrun on my opinions of Kassadin's play. I'm sure you all have your different opinions, and that's great, I'd like to hear them, but please do not make a big deal out of it. I literally made a MOBAFIRE account yesterday afternoon for the fun of making a muck around guide.

Thanks.

It's cool how everything is wrong.

I'd start pointing things out, but instead, just check this out:
http://www.mobafire.com/league-of-legends/build/bro-do-you-even-rift-349768
Everything in it is incorrect.

Turn on C2V. You have no item sequence, and some of your item suggestions are...questionable. Trinity Force, Rylai's, Athene's are all pretty terrible on Kass. And your build has 0 Mpen, so you will be just tickling them. Try Mpen marks, and Sorc boots. Armor Seals are a must in most cases. Ability sequence is mostly okay, but I don't know why you alternate points in Q/E. Perserverance is a fairly terrible mastery, especially since you skip armor for it. YOur proposed build is super susceptible to AA harrass.

I have to flee, but I'll edit more comments in later.