This Alistar build is a Champion / tower killer.
First the 2 summoner spells are my favorits, because you got clairvoyance to check incoming champions when you try to destory a Tower. and clarity to get some mana because he always need mana.

Boots.
you can take the magic resistance boots like i do, they are good because of the stun/fear/suspres resistance, so you don't being hold at tower (then it can kill you).
but you can take doge boots to improve the talents, and doge also work on towers.
or you could take boots of swiftness, to run away but i never do it.


Items.
Alistar always need mana, so get aleast one item there give you mana or mana reg.
you also need some damage to kill the tower, and i prefer the hp damage. you get some items with some hp on, after you buy impaler and deal damage like hell. but you can also buy ohter damage items (don't buy crit or speed attack, is no use at the tower in they end)
i always buy guaridan angle, so if you die at the tower you can get back to life and run away or finish the tower.

Ohter items.
when you get alot of gold by kill tower you can sell the splash damage item, and buy Frozen heat or bansish. to get more armor or magic resistance (but Bansish if you are up agains a spell caster team)(if you buy frozen heart you get full CD reduce, there also are good to alistar)

Hope you like my build, please write a note, this is my first build.