Alistar has terrible mana problems early game, I suggest that you start with a faeri charm, or donran's ring. You don't really need the 3 health pots cuz you have your own heal. Mana regen will let you Q,W,and E all day. Also by the time you get your catalyst protector, its passive will become useless (you probably have already hit lvl 18, you have health regen, and your own heal) so consider getting the negatron cloke first for the magic resist.

Otherwise great guide (love the trinity on ali)

I think the Banshee's Veil should come before the Iron Solari as your build lacks MR items.