This is a guide on AP Sion.
I used to be stuck in the 1100 ELO bracket until I started playing Sion. Now I'm 1700-1800 :)

Hopefully this guide might help out a few people.

Summoner spells should be eitherOR


In my opinion flash is must for AP Sion because it can be used both offensive and defensive.
You can use flash to escape ganks and bad engagement.
Offensively, you can open up surprise ganks with flash following with stun and shield explosion.

I feel that summoner spells are usually personal preference.
I personally can't seem to play without ghost so I use flash and ghost.

You should get at least 1 point in enrage so your farm can rack up additional hp.
Note that minion kills using your shield and stun applies with Enrage's passive.
This doesn't mean you should max enrage first.

If you look at my skill order, some of you will notice that I do not get a point in my ultimate until level 16. I do not get a point for my ultimate at level 6 because I find that you rarely benefit from your ultimate early game as an AP Sion. It's better to get extra damage from your stun. In higher level/ELO plays, its uncommon to end up in a situation where you will pop your ult and have a melee brawl with your opponent. Because AP Sion has such a crazy burst, you should try wearing your opponent down with your skills and finish them off with a flash, stun, shield combo.

Magic Penetration Reds x9 (Should be used with any AP carry caster)

Mana regen per 5 per level Yellow x9 (Sion's abilities use up a lot of mana.)

Mana regen per 5 per level Blue x9 (Sion's abilities use up a lot of mana.)
or
Cooldown Reduction per level Blue x9 (I like mana regen per 5 better)

Quintessances should either be
Magic Penetration Quints x3
or
Movement Speed Quints x3 (Makes it easier for you to land a stun on your opponent)
or
Mix of Magic Pen Quints x2 and Movement Speed Quint x1

I find thatare a must for AP Sion because of how fast he can go OOM(Out of mana). 2 Doran rings help a lot to sustain your mana.
For boots I almost 99 percent of the times usefor its magic penetration.