this is my first guide, so give me a break and try not to rip on it too much. i would like feedback if all possible.

i will be going into detail about why i choose the skills i do, why i picked the order in which to learn them, the items to get. teamwork, what to do in a team fight, Pros/cons farming skill usage and so on. i really hope it helps you in your decision to play AP Sion over AD Sion, i personally love AP just from the sheer amount of burst you get.
without further ado here is my very first guide EVER!!

to start off how about some runes. if you are not lvl 20 yet dont worry about getting the lesser runes, theyu are so not worth it at all, you will just not use them when you reach lvl 20 and have the 3 tier runes. but if you are lvl 20 or higher here is what i suggest getting.

Flat AP Glyphs
Flat Magic Pen Marks
Dodge Seals
Flat AP Quintessence

these will give you an advantage early game and will carry well into mid and late game with stacking of AP items. the dodge is always helpful. and if you want you can always switch up the mastery to include evasion to boost the dodge just a little more. i dont in this guide cause we are focusing on a more caster like Sion.

in this build i go 9/0/21
but you can switch it up a little and go 9/8/13 picking up evasion in the defensive.
make sure to pick up blink of an eye, to improve your summoner flash. get awareness for the added XP gain. and the standard caster points.

start off with a sapphire crystal and 2 health pots. this will allow you to stay in lane longer and pick up more gold.
then on your next recall pick up boots and possibly a ruby crystal.

when you get enough gold finish your catalyst of the protector,
rod of ages is your first big item, i like to get this so that you can have it fully charged before you really need it.

now if you are doing well early game with lots of kills and assists a majai's soulstealer is a great snowball item to get on Sion. but it is not necessarily needed.


upgrade your boots to sorcerers shoes for the added magic pen.
next item is your sheen, it doesn't matter what you get first but i like to get a little more AP over mana.

after the sheen, sheen is just a good item to buff up your next attack after you stun the enemy. go and get another blasting wand and an amplifying tome to build a void staff.

rabadons is your next item to buy, start with the needlessly large rod.
then just upgrade the sheen when you can. you dont always need to upgrade your sheen , but if you have the gold might as well do it. the last slot is open cause one the game is usually over by now, and two i could think of another item to put in. but you really shouldn't need to get another one.

the items are for lots of spell pen and AP so you can hit them really hard.

i max out the shield first, which will help you in farming minions and will be helpful when fighting the enemy champ for the shield gets 100% of your AP. you can swap the first skill to your Q first for the First Blood, but if you really dont want first blood get the shield
your Q is the next best choice for AP sion because it does so much damage and stuns them for your shield to get them, pretty much drops there health really quickly. the combo of Q + sheen proc/lichbane + W = dead enemy champ and if they do somehow survive hit them with ignite and watch them die running away. i dont really put a lot into cryptic gaze is because it is still really good even with only one point in it.

your E ability is not really useful for AP sion, so just pick up 1 point in it until the end and same with the ult.

pretty self explanatory. flash for best escape, and ignite for the added damage. you really could use a different spell then ignite if you want, teleport has its advantages, i just find having that little extra damage helpful if they somehow manage to escape.
exhaust is not really helpful seeing as you have a long range stun.
ghost could be a good choice if you feel like the added move speed is better then flashing over a wall. anything else would just be dumb in my opinion.

Pros
super damage output with shield and stun.
massive amounts of blocking from your shield at lvl 18
great in team fights.
great farming ability.
ability to burst down squishy champs in 2 hits

cons
a little slow early game
not a lot of health (but shield makes up for it)

makes sure that when a team fight starts that you target the enemy carry with your stun.
have your shield up and ready to detonate on the whole enemy team, this should put a huge chunk into all of their health and make it easier for your team to win the fight. when your team is at about half pop your ult, it will go a long way with helping your team. the added life steal wont hurt, the ult also heals your team and i dont need to tell you how nice it is to heal your whole team in a team fight.

the way this build works is by giving all the power into your shield and stun to do the most damage. when this is done you will be able to clear any creep wave with just your shield. a lot of sion guides are all based on AD life steal and attack speed. this is great because the ult and e work well with those. but i find it is harder to farm or kill champs before they can run away. with this guide you can drop them really fast. run up with your W detonate it they start running your use Q takes another huge chunk away and stuns them, finish off with auto attack and they are dead.

sion is a great farmer, the shield he has will detonate and damage all that surround him. with some AP you can take down an entire wave of creeps. and with the E activated you get health from all the kills. sion only gets more beefy the more he kills, last hitting is your friend and your AOE shield burst is great for hitting all the low health minions.

So if you follow this guide then you should be able to do whatever it is that you needed to read this for i dont know I'm a girl and need to be in the kitchen doing the dishes. but when no one is home i sneak out and play LOL i have found that this will win me games fast enough so that i have never been caught out of the kitchen (or bedroom) AP Sion can clear creep wave and push lanes super well, and in a 1v1 or dare i say it a 1v3 he can hold his own burst them down then when he is low pop the ult heal back to full and repeat. i hope you liked the build and feedback is most appreciated, now i have to get back, i think they will be home soon.