This AP build for Alistar

First learn the 3 first spells learn Q first then W and then E. After that only learn Q until you cant anymore (Learn Ulti at 6) When not able to learn Q then learn E. Headbutt aint a important spell to level up asap level that one to full when the rest is full.

Flash is good to charge an enemy. You run to your enemy and flash so you get behind him and headbutt him and that makes it alot easier to kill him (specially if you got a teammate there.) Ignite is good to get kills. Many times they will get away with just 30,20 etc hp left so thats why i love having ignite when playing Alistar.

Are basiclly AP items you want the Crystal Scepter for a little more health and you also get AP :).

Learn to use your Flash so you get behind them and headbutt them further away so you and your teammates can get a easy kill :D.