Last 6 items are your decision, if the enemy is too AP or too AD you counter them with one of these items.

Cooldowns / Mana Regen / MR / Armor / Around 2.5 3k Life

Either CV / Flash or Exhaust / Flash Or Exhaust / CV if you really dont need flash and u wanna be op.

Runes are for Bottom Support , all you need, Gold per 5 / Armor / Cooldowns !!!

9-0-21 is what I think a really nice support sheet.

I Max slow and cooldown reduce first to be the best support possible,when your jungle gank and you slow like hell.he cannot escape.

Pros:
-Fast,Slow Long time.
-Amazing ult you can troll the enemy when they think they can give you a last hit and you dont die.

Cons:
-No shield
-No heal.

Remember that you are ranged you can harass at low level,it will make the difference, trust me.