Make sure that when you get the gold for your tear of the goddess you go back and get it so you can work on getting that max mana full. So the way I use this build is to allow me to maintain my aura of damage and to make my ult do as much damage as possible. You don't have to use all the Archangel's staffs you may need to trade one out for a void staff to help with magic resist.

btw this builder is not counting that the ap from the archangel's staffs stack so the ap is some where around 1.1k