Basic AP caster build. If you've seen one you've seen them all.

here are the stats, because for some reason they weren't showing up properly

Health 3566 at 18
Mana 2200 at 18
Health Per 5 secs 14.4 at 18
Mana Per 5 Sec 27.8 at 18
Armor 80.5 at 18
Dodge 0 at 18
Magic Resist 30 at 18
Damage 94 at 18
Critical Chance 6.25 at 18
Ability Power 707.39 at 18
Armor Penetration 0 at 18
Magic Penetration 68.55 at 18
Movement 380 at 18

Marks of insight really help early game especially after you get magic penetration boots. With these marks and boots you should be able to kill pretty much anyone in your lane which will give you a good amount of gold to buy Mejais and strt stacking AP early.

Seal of clarity are especially good for this item build and masteries which are generally lacking on mana regeneration. Annie is mana hungry for pretty much the first half of the game, so as you level you keep stacking additional mana regeneration which will give Annie the ability to stay in longer farming and ganking.

Glyph of force and quints of potency allow for a stronger player at both beginning and end game. The flat AP stacks help to get kllls and stacks early on and the lvling AP allows you keep a slight advantage over your opponents as long as you keep using the elixrrs of brilliance.

Boots first. Gives you additional magic penetration, which coupled with you flat AP quints and marks of insight allow you to get several kills early on. This give you enough gold to rush Mejais and start getting stacks.

Next is Rod of Ages. Great all around item. Is a central build item for Annie, giving her survivability, mana and at full stack 80 AP.

Next is Rylai's Sceptar. Gives Annie a big chunk of HP, a slow and 80 AP which coupled with elixirs will ensure many many team kills and assists. After Rylai's is built you should be pretty close to 20 stacks on Mejai's.

Next is Void staff. Sometimes I buy this before Rylai's but only when the other team is stacking magic resist. Void staff is pimp, no doubt about that. With an extra 40% magic pen you should be getting kills left and right.

Next is Deathfire cap. Lets be honest, this is an AP build so the kudegra will certainly be the extra 155 AP and 30% boost to AP.

You have all your items now and from here you should just continue to buy elixirs and stay with the team fights.

Obviously you have to play against your opponents though. If your getting pwned and you can't farm, kill or assist properly you should probably stay away from Mejai's. Additionally if you are having trouble getting gold for the aforementioned reasons it might be good to buy a Banshees or Thornmail.

Straight up Flash and Ghost combo. Give me two escape and chase options. I really don't see why you would use anything else with Annie. Maybe ignite for early kills, but Annie does so much damage anyway that getting ignite should be a moot point.

You want to go mid. You have an excellent range and you level quickly using disintegrate to last hit minions. Annie does get harassed alot, so do NOT over extend. You probably should not be trying to push the middle turret unless several of your team mates are trying to do the same. Play conservative at you turrets and use Tibbers to harass. Might sound like your wasting an ult, but every time Tibbers kills something you get gold and XP which means that you don't have to be in the middle of the fight taking damage. Additionally, buy health pots so that if you are getting harassed early on that you stay in the battle. If your low on mana and have to blue pill, try popping and pushing with Tibbers to your opponents tower. Once youve pushed, blue pill and Ghost back. Should give you more than enough time to go to base and back without your turret taking any damage.