Not Updated For Current Season
The runes are very important for this to be a viable solo tank / bomb. The health re-gen from the get go will keep you in your lane for as long as you want. You are going to hug your turret because Sion's greatest asset at this point is his "stun" "shield bomb" combo.
Lets go over the items 1st.
1. Regrowth Pendant - 15 health re-gen every 5 seconds. Huge.
When at your lane. Save up till you have enough for boots of swiftness and another Regrowth Pendant.
2. Boots of Swiftness and Regrowth Pendant.
Now you have the capability to run in stun and drop a bomb on the idiot that thought you were hugging the turret cause u were scared.
3. Force of Nature - Sions best friend.
4. Heart of gold. for the gold...
5. Randuin's Omen. Now team fights will swing into your favor heavely. unique active owns face.
6. Nashor's Tooth. - This bad boy will give you some more mana re-gen some much needed ability power and the all important cool down reduction.
7. Lich bane
8. Rylai's crystal scepter - to give you around 5k-6k hp
So if you are looking at the stats above your wondering "how in the hell do I get 5-6k hp. Well at lvl 3 u will have your Enrage running non stop. by lvl 11 or 12 your shield bomb should be a 1 shot kill to any and all minion groups. Every kill Sions max health goes up by 3 This adds up very fast.
With Force of Nature restoring .35% of your champions health every second. You are an HP re-gen machine.
Just play safe and call in your jungle to relieve you when u need to go back for items.
Cheers let me know how it goes for you. I find even if my team blows I come out with positive kdr, because the 2 foe's i'm going against think i'm an easy target. They die soon after with turret / stun / bomb dropped on there heads.