I started league not to long ago, at the beginning of season 3, I'm not even level 30 yet as i don't play as often as i like to, but i have had time to fall in love with Sion, whilst scouring the internet i noticed that i could not find a single guide for him that was not outdated, i long considered this, i thought maybe Sion was not good anymore, but i do well with him, so i guess he just needs a little love. This is my first guide, so go easy.

TLDR?
Welcome to the guide of Sion, The Undead Champion

Sion is a great combination of health and damage output, if you augment his critical ability and his attack speed, you make things downright unfair, not much to say on this other than he absolutely need the attack speed and benefits greatly off of the crit bonuses.

As stated in runes building attack speed is needed, but here we can also bring up his tankyness even more.

Sion benefits from this great combo of life steal, damage, and attack speed and all around help, it brings stats way high. just look at the rundown at the top

Sion spells mostly focus of winning a team fight of toughing through a 1v1 where the odds are against him, his ultimate is extremely powerful and can dwarf even the mightiest of enemy champs, i recommend using his stun as the enemy trys to run away instead of when you first come on them

Pros
He is amazing at 1v1 or heavy team fights(3v3 or more)
He can sustain so well
Great at pushing

Cons
He is very mana hungry, use ability's when they count
He is very slow at first
He cannot tower dive well

He works well with anybody who has heavy CC or an assassin to get the last strike he can't get

Please give me feedback i follow this guide as well, so improvement in items department will help me
Stay thirsty my friends :)