Not Updated For Current Season
This build is for Sion as a mage. However, he fulfills a unique role, in that he's somewhat of a mage-tank.
Flash is necessary to complete what's a devastating lane opener, especially with a decent lane partner. First, apply your shield, and wait until there are about 3 secs left. Flash out of bushes, apply stun, shield explodes, Ignite, whack, whack + whatever your lane partner can do and it's usually a kill.
Certainly not complete, but I'm confident that its a good build so far.