So this is one of my builds I use when i play Sion. Thid build is a different way of playing him, Items a mix of a tank and AP dps build and it is effective. I will assume you have played sion and know his spells and how to play him in a ordianry dps build. So i will not go over his spells and what to do and when to use them etc. If you want that information(aka you are new with this champion) I reccomend you to look up a different guide for some basic sion tips etc. AP on Sion is one of the harder playstyles of him and are not for new players,a AD or AS build is much more for the unexperiencd sion player.

1 more thing i want to point out before i start is that you will be very dependent on your team! Team your self up with a cary such as Master Yi or ryze. Your job is to provide support and be a meat shield, try to provide them with kills. That is the way to Victory!

Have fun reading.

Since the patch where zhonyas ring got thrashed and we got 2 new items, this section is hard to do. There are alot of different ways you can build a tanky AP sion after this patch, but the 3 core items still remain the same aka 2 Rod of Ages a pair of boots(will get into what pair of boots you want further down) and the new all omfg gief more AP item, the Rabadon's Deathcap.

So before we get into the more advanced finetuning of this build, you should go for these core items. Do not start building anything else untill you got these four items.
So your bag should look like this:.
These are good all around this build and is my choice for most of the games i play since i like outrunning my opponents. You will be fast in these boots and if you often find yourself chasing your oppnent, then pick these.
Next up is Berserker's Greaves. They give you 25% AS. Pick these if you are going to pick Atmas impaler as 1 of your 2 items. They are not quite as good as the rest if you dont have atmas, So if u buy these, but atmas.
Ionian Boots of Lucidity. A good pair, gives you a cooldown reduction. So CDR allways nice to have, escpeically if you are going for a heavy AP build (Zhonya's Hourglass + X) Will work nice with this build no question about it. Get these if the enemy teams isn't building Magic resistance and you don't need to run around alot. They are good, Long live the Ionians.
Sorcerer's ShoesAswell good for this build since you are building AP after all. But I vould still say there are beter boots then this except when the enemy team are building magic resist. If they are pick these. If not pick something else! If you want the extra dmg output pick CDR boots, going for atmas and want dps? pick AS boots, Heavy stun/taunt/CC team? go for mercurys. U get the point. Pick these if the enemy team are building magic resist.
2 left. First out is Mercury's TreadsSome magic resist and CC reduce(except knockups and silence) A good pair if you are up against a CC heavy team, only against a CC heavy team. Other then that they are worthless.
And last up is Ninja TabiThese are the tank boots against melee dps. 12% dodge+ the dodge from the specc=14%. Doesn't sound much but it is. Pick these against melee teams, will reduce their dmg alot and you will notice it.

Leaving the boots and diving into the hard part, what do we want to pick for the last 2 items.
The choice stand between 4 items.
Banshee's Veil, Zhony's Hourglass, Atma's Impaler and Guardian Angel.
These are all good items combined with this build.
Atma's gives you alot of AD since you will land on 4k hp + your enrage spell wich gives you even more HP.
Guardian Angel is the ultimate tank item and i almost allways pick this as 1 of my 2 items.
Banshee's Veil gives you more HP, more mana, Magic resist, and blocks a spell. I go for this if i face alot of spell casters, or a team with stuns since it will block 1 of them.
Zhony's Hourglass 2 sec invulnerability armor and more AP. A good item, will work perfectly, and those 2 sec u get from the items, will save you're ***, if you remeber to use it ^^.

What you pick here is up to you and it should reflect how u want to play him. I personaly picks Guardian angel and atma's/Banshee's. Since this after all is a tank build.

So as i mentioned before playing this build to perfection will take some practice. I will not explain what every spell i mention below does since i assume you know this allready.
Also to add here is that you are very dependent on who is in your team. Laning witha support is a bad ide since you do not put out enough dps to fill up a dps part. Try to lane with a cary or atleast some1 who does dmg at level 1. Your stun should attract cariers without one so you should be fine. But once more since its so important for you and your teams succes, pick a good laning partner!!!

Early game
A tip here first. Have your lane partner pick up ghost or TP as a summoner ability(or boots if it's suits them). If you both got TP, use them on the tower and get into their bush. Or pop your ghosts( this is prefered since its a long cd on TP and its more usefull early game then ghost) to get into their bush( by their bush i mean the bush that is closest to their tower). Most people wont expect 2 ppl in that bush say 40s since the game started, and because of this they will be unprepared and a easy FB can be taken here.

In this phase your job is to throw a stun out, and explode stuff with your shield. Get stun at lvl 1 and shield at lvl 2. Its important here to not waste your mana! Use yours hield to farm creeps, since the shield absorbs the dmg you vould get from enrage and its a great last hiter. If you get 2+ minions with a shield explosion, it was worth if. If however you only get 1 it was a waste of mana( If you didnt get the dmg of on a enemy champion).
Remember, you are very strong early game beofre level 6 and every1 gets their ultimates. pop your shield of before you run in so the "cant explode" timer goes away.
When you go into combat, initiate with your stun. then when you get there blow your shield up. And then you dont have much else to do then auto attack or retreat. It all depends on the situation you are in.

Mid game
Mid game is usualy between lvl 8-13ish or so. Mid game ends when you start running in groups of 4 or 5 (aka ganking the **** out of the other side).

Before this running for ganks in mid or the other lane is a good tip. People love your stun and since you got a deasent amount of HP you can take tower dmg for a short period of time. Your stun is your friend and so is the chat. they are you key to succes and getting some kills/assist. Dont forget to kill off the ghost camp and or wolf camp. These camps should basicly be one shotted by your shield.Stack up your health with enrage and shield(you do get the proc from enrage if you kill a creep with the shield explosion). Remember to watch the minimap and the chat so you see if someone is mia(or ss if you play on EU servers).

Late game
This part of the game is your time to shine. You should have both your rod of ages and atleast building on your zonyas here. Your shield has a lot of health and dmg and so should you. Here it's almost only teamfights and that is the way to win, Teamfights and ganking. Map awarness and mia calls is important and not taking stupid decisions( aka running and attacking their inhib tower with your team at your base and their team mia).

At team fights your job is to have your ulti hop to provide som healing to your team, do heavy aoe dmg with your shield and stun their carrier so you can get a fast kill on him. And ofc to run in first with your shield up to take the initial burst. There is the same skill order as in early and mid game with one exception, w8 with your stun untill theri carrier shows up or your team is in position to deal with him/her fast. Kat is a good example of this. W8 with the stun untill she pops her ulti to interrupt it and then kill here. or w8 for fiddle to dive in with his ulti, stun him and run out of the aoe. You will be very dependent on your team but dueling a enemy is possible unless that hero is a cary champ.

So to sum things up a bit, farm up your enrage, go for ganks, use shield before you run into fights and pick a good laning partner! Good luck and have fun trying this build out, its a bit different but is realy fun to play.

Made by:
Akaxor
PS. If you down vote do me a favor and comment on why you did so, it will help me improve and this guide to do so aswell.
If you want to play a game with me, i play on both eu and us servers, add me(akaxor) and we can play a game or 2. also check out my nasus build(link should be on your right side) and my future builds there.
Comment and give them a thumbs up!

Cya around, Akaxor

2011-01-12:
Redesigned the guide using the new design by mobafire. Its lovely!
Also added an explenation to the runes.

2011-02-19:
Rewrote the whole Items section
Tock away chonyas ring from the build
Added more item builds
Removed the Runes section since it was porly written anyway