This is the Sion build I use when I play with Blitzcrank or Singed as my tank laning. It's a combination of handpicked masteries, the generic Rune Book for any AD character, and an item build from an AD Yi that works incredibly well with Sion. Played properly, this will yield KDAs in the 20/5/20 range.
The Key to playing Sion properly relies entirely on your use of your PBAOE shield and knowing who and when to stun. If you do not have these two things down to a science, you won't do well regardless of any build.
This runebook focuses primarily on Armor Penetration, MP5, and Crit.
Armor Pen: With Sion's innate lifesteal and massive HP pool, Armor Pen gets through other melee carries, allowing you to outlast their attacks, while dealing damage. You should be able to shield in an engagement and come through the engagement with a melee carry on 3/4 to full hp.
MP5: People will argue that MP5 is a wasted Stat on Sion, but I believe this is based on his late game performance. In order to lane for long periods of time early game, and farm the gold you will need to get all your items, Sion NEEDS this MP5. Late game it doesnt do you much good, but by then your items will support you fully.
Crit: Lifesteal crits = more HP in melee engagements, nuff said.
Standard AD. Nuff Said
The most crucial part of this skill selection is the order of the first 6 abilities (when isnt it).
First you start with Death's Caress. This is useful, not just for minion kills, but also in ganks. Hide in a bush, activate, wait 3, run out trying to reach middle of creep and opposition, explode. Early game laning it will nuke the creep and reduce hp of opponents by about 1-2 bars. Very useful for discouraging approaches. It can also be used defensively to lure opponents to your tower. Overextend, activate, run back, let them chase. If it pops, they take damage, if it absorbs their attacks, even better.
Next is Cryptic Gaze. This will be used to stun opponents near towers, disable heals and stop running opponents who are low, post PBAOE.
Third, acquire Enrage. Turn it on, and never press this button again. This should be on at all times. Use your shield to weaken mobs, and then kill them with a melee strike. This will farm hp for late game.
Fourth through fifth. Pump your shield. As it gets stronger, your lane presence will intimidate. Defense and Offense. No brainer. You only need 1 rank in cryptic gaze, strictly for the stun, and you only need 1 rank in Enrage for hp farm early game. Forget the rest.
Sixth, Ult. Sion uses his ult for 2 things: 2v1 fights and tower breaking. The haste from your ult melts towers. I usually save the ult for breaking towers. Breaking T's wins games, killing opponents does not. in a tough spot post skirmish in 5's, you can use this ult to refill your hp on minions.
After Six, rotate between shield, enrage and gaze. In that order of priority.
Exhaust. Use this after a stun to slow a runner or if your stun is on CD.
Teleport. This item build requires constant returns to the shop. Teleport will help you gank, cross lanes for D and get back out onto the battlefield with 0 downtime.
First buy is Doran's ring. I didnt bother adding it to the final build, because you will only use this until you can sell it and acquire the greaves. The ring is necessary to fuel your early game PBAOE spam fest.
Greaves: Sion moves extremely slow, this is why you have to Tower Hug until you get the boots. This begins the attack speed part of the build, paired with your ult is your AS/LS early game.
Inf Edge: This comes next, it takes your Speed and puts it to good use with your ult. Here's your bulk of AD and crit. EXTREMELY EXPENSIVE. This is usually pieced together, it's not a single buy. Priority is the BF Sword. You can have this built before mid game if your ganking is decent.
Blood Thirster: AD and Lifesteal pump. The priority here is Vamp Scepter.
Recurve Bow: Get this before late game. You need the speed. It's extremely important.
Starks: By now you should be getting up there in kda, and your gold should be silly. No team fight is complete without you and no one should be initiating until you are there. Starks is a team fight item. Nuff said.
Speed Pots: Grab this to help destroy towers and Lifesteal like a beast. You should have these on hand any time before or after starks.
Last 2 Items. They don't matter. Sometimes I armor vs. magic, sometimes I grab CDR. It's up to you, the base of this item build are the prior Items. Usually game ends before you can complete the build anyway.
Remember, masteries are always to taste. Runebook should be generic for AD so you dont have to switch it when you play different AD based Characters. Skill Selection priority is Shield, Gaze, Enrage, Shield to max, and Ult. The build is speed and lifesteal with crit primarily.
Shield is for Ganks (from the bush), Defense and Creeping. Always self detonate near the middle outside edge of a creep, so as to get enemy champions with it.
Gaze is for near tower stuns, heal disables, and ult interrupts.
Enrage is used in combo with a melee strike finish on creep, post shield use.
Ulti is for 2v1 situations, Farming health off creep after a 5v5 3v3 situation or for Tower breaking, with Tower breaking being priority.
Sion is a Hybrid AP,AD TANK/CARRY This build focuses on making him fast AD melee with HUGE HPs late game (so a bit tankish). This will keep you alive while you destroy the enemy opposition quickly. Sion is basically a tougher Yi, and when built right, has Yi's Attack Speed with a tank's HP.
I hope you all enjoy this guide, and playing Sion, I know I do.
If you like this guide, keep an eye out for my Singed build coming soon.