My build usually goes
->
->
->
->
/
Of course build depending on whether or not you need early MPen. No one builds MR go straight for DCap after Morello, otherwise go Liandries.
Good HP/Mana boost from RoA so you dont worry about running out of Mana.
Max CD + Mana Regen from Morello = Nonstop Spam + Ult every 48 seconds.
Liandries synergizes well with your kit with its % Health Damage
Its MPen + Void Staff MPen allows you to still shred tanks.
I dropped Zhonya's a long time ago, while its passive and bonus armor are great the fact that you have no escapes makes it pretty irrelevant in most situations, you Zhonya in a team fight and immediately when its over your still dead.
I go 21/0/9 on my Masteries, improved recalled, increased movement speed, 10% CD on Flash and Ignite, and Biscuits are great as they give some Mana back too.
As for Runes I got Hybrid Marks because your voidlings benefit from ArPen, you only lose 2.3 MPen as opposed to straight MPen Marks but gain 8.1 ArPen. Afterwords I split my seals 5 Mana Regen/4 Armor, then I finish with 9 AP Glyphs and 3 AP Quints