First of all: I did this for a friend, I don't really care if the guide isn't great.

Also: I swapped out 2 items, and haven't yet modified the guide around that fact. That being said, Sion is very much like Nasus in my opinion, except their skills are mixed around, and slightly different. Despite not being played very often, he is rather good at dueling against melee champions due to his ability to shield, stun, and then walk out taking 0 damage. He is also good at split pushing and then getting away with it, as long as there isn't more than 1 or 2 people coming after him.

Pros:

• Ultimate heals allies
• 90% AP Scale on shield
• Easy to avoid being dived
• Scales Health with CS
• Decent Splitpushing

Cons:

• The range that the ultimate can heal someone from is little more than melee range
• No Escape abilities
• No AoE except your shield which can be cancelled
• Shield is often bursted down

We get Greater Mark of Scaling Attack Damage to increase your damage, since a lot of the items we get give attack speed and you need AD to benefit from that. Greater Seal of Scaling Armor and Greater Glyph of Scaling Magic Resist provide defense that is much needed, and since the punishment you will take later is much stronger, we make them scale instead of the flat runes. Greater Quintessence of Life Steal provides sustain in the lane, and this allows you to stay longer so that when you recall you end up with more gold.

We begin with Death's Caress because the shield allows you to farm easier and it blocks whatever they may hit you with early on. Next we take Enrage because from then on you gain maximum health every time you get CS. We max Enrage immediately because the health you gain per CS increases per level, and your AD increases every time it levels. Next we max Death's Caress because the shield is quite nice, but having maximum health increased is of course better than a temporary shield. We only level Cryptic Gaze at Level 3, and then it's your last skill to max because the stun's duration doesn't increase. Obviously we max Cannibalism as soon as we can. At full build you heal 348 Health per second while it's running, and any ally right next to you gains 264 health per second. Alternatively, with Bloodthirster instead of Guardian Angel, You heal for 653 health per second, and your ally heals for 389 per second.

Mercury's Treads

The Tenacity is a must have on any champion, and the magic resist is nice, and of course you have to have boots.

Trinity Force

Good item for hybrid champions, increases your AD, AP, AS, and your defenses, as well as some other utilities. Rage makes it easy to stick to champions who are trying to run away, as well as you having a move speed increase from the item itself. Spellblade Makes for an amazing last hit on escaping enemy champions, use Cryptic Gaze on them, and then run up and land the final hit with an automatic critical strike due to this passive, which gives you 200% AD on the next hit.

Atma's Impaler

Due to the maximum health increase that Enrage gives you, this item puts that into extra AD, it gives you crit chance, and armor! If you get about 150 CS end game, then this item gives you 44 AD. It isn't that amazing, but the crit chance and armor together make this quite good. Also, after that 150 CS, you will earn .045 AD for every CS. 23 cs per 1 AD, about 4 waves of minions to get 1 AD. It's not really that hard to farm either with Death's Caress having the potential to kill the whole wave with 1 explosion.

Guinsoo's Rageblade

Grants 40 AP and 30 AD. This also allows you to reach the max attack speed with your ult, or get really close without it. If you continue to hit them, then you gain more AP, and then your shield is worth more. It also has a nice mechanism to save your life, because when you fall below half hit gives you 10% LS and 10% Spell Vamp, making it even harder to die.

Nashor's Tooth

Provides 60 AP and .5 to your attack speed. It also gives Cooldown Reduction which is always nice, and allows you to only spend 6.4 seconds without your shield at a time. In addition, your basic attacks now deal 15 + 15% of your AP magic damage per hit. Since we build plenty of AP, this is really nice.

Choices for Last Item!

Guardian Angel

Provides 50 Armor and 40 Magic Resist, and has a nice passive. Good item if they are a balanced team and you are not ahead.

Bloodthirster

Provides near 20% life steal, as well as 100 AD. This is a great damage item if you are ahead and don't need to be more defensive. Buy it instead of Guardian Angel, because the other items are pretty important.

Frozen Heart

Good defensive item vs. a team that has mostly AD, or their APC can easily be destroyed in a teamfight, leaving you with AD enemies. Otherwise take Guardian Angel because it is more balanced. This also provides CDR to take you to the maximum, and since you should have Nashor's Tooth you will now only spend 4.8 seconds at a time without your shield up.

Spirit Visage

Provides Magic Resist for an AP heavy enemy team, which doesn't happen very often. However, if they have an AP Top and Jungler, then take this item. It also gives you some regeneration, which isn't much, but it is nice. The passive also makes it so that you have 79.2% life steal during Cannibalism and while Guinsoo's Rageblade has its life saving passive going. That's a lot of health to regenerate per attack!