[Hermes]

With AP champions you focus solely on ability power and utility, you never ever work with AD. This is not counting hybrid champions such as Akali and Jax.

A sample AP build that works for just about any mage:

Liandry's Torment, Rylai's Crystal Scepter, Rabadon's Deathcap, Will of the Ancients, Seraph's Embrace, <Your choice of boots>


I also like Rod of Ages and Hextech Gunblade a lot, but I mostly play people like Nidalee who actually enjoy some basic attacks.

When I build my Orianna, a more mana-hungry mage, my build looks more like:
Seraph's Embrace, Rod of Ages, Liandry's Torment, Rabadon's Deathcap, Rylai's Crystal Scepter, Athene's Unholy Grail.


The core items for most AP champions are: Rabadon's, Rylai's, Liandry's. The rest is all interchangeable situationally.