My goal with this Sion build is to demonstrate that not only can Sion split push and win extended trades against most champions, but that Sion is not just a full AD one-shot champion, a full tank meat shield with some cc, or a brain dead split pusher who runs into towers with ult all game, but that Sion can be played to win trades that last longer than half a second. Getting first tower is easier than ever before with sheen activations, and one of the best top lane wave clears early.

Resolve:
Grasp of the Undying: The idea behind grasp is to make the one or two autos you weave into your combo have more impact. The sustain is not negligible either, and the health gain can really add up versus a immobile tank like Nasus top lane.

Bone plating: A must take on most champions running resolve these days, it easily outclasses the other runes in the set. You may however swap it out for demolish for extra tower pressure.

Chrysalis: The extra 50 health starting the game is super effective at surviving trades, and can give you an upper hand in many fights where the opponent is not running resolve. Can be swapped out for second wind versus ranged top laners who have lots of poke.

Revitalize: This rune is pretty good, as it increases the shield power on your W, and is essentially the best rune in the last row of resolve.

Inspiration:

Biscuit Delivery: These biscuits are a godsend, they allow you to get free many per one consumed, adding up to a free 160 mana at 12 minutes. This mana can be the difference between casting an ability and not casting one. The healing and mana regen is also effective in lane, because without it you cannot effectively ability spam your opponents out of lane.

Time Warp Tonic: A good compliment to biscuit delivery. It extends the heal and mana regen duration of the cookies. It also extends the heal and mana regen of your corrupting potion. The healing between these effectively makes it impossible to lose most lanes.

Your itemization is pretty lane specific, but it can be broken up into three sections.

Vs AD Top Laners: Iceborn gauntlet provides a slow, extra damage, armor and cdr. Everything you could want in this lane, rush the shield part if behind, rush sheen if ahead.

VS AP Top Laners: Abyssal mask provides extra damage, magic resist, health and mana, and cooldown reduction.

VS Fiora: Bramble vest and then Iceborn Gauntlet

With this build I like to play two different ways.

If you/your team is ahead: I prefer to keep pressure on towers top/bot and save teleport to join fights with my team. Many people cannot do enough damage to Sion to contest his split push, and can't catch him out without flashing to stop his ultimate.

If you/your team is behind: Stick near to your most powerful member, whether it be Mid/ADC and ensure that you keep the enemy off the back line by saving ultimate to point blank cancel their engage. Kite the enemy away with your slows and cc. However if your team has someone like Janna who can peel for you, try to flash ult Q their carry, allowing your team enough time to stack cc or murder them.

Q Max: A good majority of games this is the best choice to go. The base damage it has is almost unrivaled by any other ability in the game, and its cc is comparable to that of the Morgana's Dark Binding. The duration of the CC increases the longer you charge it, as does the damage. Try to not be greedy and always just go for the Q the moment its able to knock someone up. However in lane attempt to force flashes by holding out your Q for maximum cc and damage.

W Max: This is a good choice for a lot of losing lane matchups, as its able to negate a lot of bad trades, and can be used as a get out of jail free card. Its damage is not negligible either, since it does %HP damage, it will chunk an enemy who lacks MR. This works good as a surprise because many people get early armor vs Sion.

E Max: This is not as good as it was back pre-E gutting. However it can still be used to safely secure farm at a distance, and the damage itself is not bad because people will not expect AP damage.

Once you have Sheen you can do some pretty nasty damage in one combo.

Attempt to begin every combo with an ultimate or an E.

If you hit your E use your ultimate to close the gap, while ulting use the first activation of W. Once you hit your ult charge a Q as long as you can comfortably do ensuring they're crowd controlled again. Apply your Sheen and Grasp at the same time as you reactivate your W to do a huge burst of damage. This can one combo squishier champions, and easily take a tank from half life to 0.

If you hit your ultimate first, immediately shoot E and begin to charge Q. While your Q is charging use the first activation of your W. Once your Q hits combine the pop of your second W activation with your sheen and grasp auto attack to do a huge burst of damage.

Pros:
Big Damage
Satisfying kills
Aura buff to all AP users including yourself
Able to one shot, while they cannot one shot you.
Able to match split pushers, or split push yourself.

Cons:
Loses hard into some matchups
If you fall too far behind, its a less effective build
Can be kited easily without ultimate.