Quote (Protectah @ 14 Jan 2011 18:55)
if you build one you should build it first or it wont be charged throughout the game
I usually manage 2 stay alive a lot with karthus. And by that, I don't need life. So I prefer mana > life.
And at the beginning your defile cost a huge amount of mana.
But sure, if you notice early in game your tank is crappy and you play aggresive. Go for RoA then!