The items are pretty straight forward, I think. They are all found under Ability Power save the shoes (Movement) and the Thornmail (Armor). One thing to note here is that while the Thornmail is not typical of any build for a mage such as Annie, it can prove quite useful later game if you find your self taking a lot of hits. If the other team is not focusing you, then you can switch it for another Rabadon's Deathcap for the extra Ability Power which is very recommended. The Void Staff and the Archangel's Staff order can be reversed if you find yourself running out of mana too quickly early game. Also you can purchase consumables to boost your mana, but they are only temporary. The idea behind these items is that the summoner already has the skill to make up for their deficiencies and maximize their strengths.