Please don't build Nashor's on Diana. It's really not that good on her.
Core; Zhonyas, Abyssal and Deathcap
Situational; Lich Bane, Ryalis and Athene's (I know people are gonna argue with this one, but Diana is pretty mana hungry and she benefits a lot from having Athene's, even the CDR is nice). --- Going to church doesn't make you a Christian any more than standing in a garage makes you a car.