Annie is in my opinion the best mag for how little IP she costs. She is not only great in team fights becuase of her ability to initiate with her passive, but her burst damage is unreal. I would reccomend her to anybody who is new but I use her all the time in ranked matches and normal games. My normal win percentage with Annie is 82% and ranked is 62%.

Disentegrate- Main ability and level it up anytime you are able to. This spell is key when nuking your opponent

Incinerate- another main ability hen nuking and requires key placement. I would rather use tibers for initiation, but this spell could also be used with her passive to AOE stun the whole enemy team.

Molten Shield- don't worry about this spell until your done ranking your other three abilities. However, this shield is a free thornmail basically, and helps a whole lot. Not only does the armor and magic resistance help, you can use this spell and incinerate to build stacks of your passive.

TIBERS!!- He's a bear, badass one. Huge damage when dropped and every second when he's in range of enemies. Use this spell when you have passive ready to initiate fights with a full team stun. This spell make team fights unbeatable for the enemy.

Flash- use for defensive at early game. Sometimes I use this for troling people with tiber's stun, just pop in and cast and score an ace.

Ignite- Key for spell rotation, does great dmg to run aways

These are the standard runes for Annie and almost any mage. I take magic pen marks and quints to lower the enemy's resistance. Rather than taking AP for these slots, this is becuase magic pen IN ALL offers more dmg when casting on an enemy, especially if not a tank. I take flat health seals for a defensive stand, especially early game because Annie excels at mid lane or solo laning. AP per level glyphs is the cherry on top, offering a little more bang for your buck on her spells.

Alternatives- Mana per 5. WHY NOT?- Dorans Ring is enough, plus last hitting minions with disentegrate refreshes it's mana. If you play more aggressive early game, this could help, but I play aggressive and find these not nessecary.

CORE SET
Dorans ring, Sorcerer's Shoes, Rod of Ages, Rylais Scepter

or

Dorans Ring, Sorcerer's Shoes, Rod of Ages, Rabbadon's Deathcap

Either of these choices for your core set are great, 1st gives more defensive stance yet 2nd gives more offensive.

After the core items are built and bought, I recommend getting Morellos Tome for the AP and CDR, and Abyssal Scepter for the MR AP and MPEN.

ALTERNATIVES- Mejais Soulstealer- great item but if your new to the game or playing mid/high elo it it pointless because you will not get many kills for it to have a better affect than other items
Void Staff- Very viable option becuase it will make your rotation hit like a bulldozer. This is not an item to turn down at all and half the time I fit it into my item build
Zhyonas Hourglass- Not bad, I would only buy if it is end game and nothing left to buy becuase it is expensive, but is very good for the armor and AP (maybe the active but eh)

Annie is great at initiating, always know that. If there is a Sona, Amumu, any champions with and AOE stun or what not is a great teamate with Annie. Annie can have an AOE tiber's stun and if Sona and Amumu perhaps do there AE stuns after Annie's, it is impossible for the enmy team to win fights. It will be gg from the start.

Pros
- AOE Stun great for initiating
- Good farmer
- High burst
- decent defense with items/molten shield
- Amazing at solo and mid lanes
Cons
- Could be a little reliant on mana if aggressive early game
- Targeted alot (hence flash)
- Have to be a master at her passive to be unstoppable in teamfights (during teamfights that is, for timing to get an aoe stun with incinerate)

In all, Annie is a great teamate, great laner, and great mage. She has the ability to initiate, do amazing burst, and play defensive. She also can tower dive with Tiber's, but that is situational. I hope you enjoyed this build for Annie, although she is highly underestimated she is highly overpowering.