There are a lot of ways to play alistar, but really I think what determines your item build should be how the game is progressing, the hero mix, and the masteries and runes you go. Since I am focused on Utility spec, with flash and ghost, and a bit of defense the CD% reduction from utility and the extra mana regen helps aid my build with chalice. Getting early mana up and shorter CDs also helps my build.
I typically am running around towers moreso than hitting them to keep their ranged dps back, and melee so that my partner in the lane can hit the tower freely with the creepwave. This is a bouncer like mentality, that keeps pressure on my opponents while helping us down towers. Alistar will always attack slow regardless of Sheen etc. so there is no need to rush it or grab it for last hitting if you are already good at last hitting, and ganking opponents in lane.
Frozen Heart / or at least Glacial Stone (shroud? always forget name) gives you a huge boost if you can save the 1600+ gold for it, the sage ring, give you mana to fuel chalice and CD reduction to keep the pain going.
I may be one of the few to max headbutt first, as it seems to make a difference in team fights, the bit of extra damage makes the kills quicker when I punt them back to the vultures, or can often times yield a lot of gold in last hits for kills. I don't try to steal from the carries, but if I am in range and can seal the deal I will.
If you want to have a nice Item collection by the end game, or are going more straight team support defensive like Bait (which is totally recommended and commendable) this is a great build. If you want to be a little more seat of your pants and be a bit more self-centered as a tank, try chalice/boots/frozen heart(sage ring first), I end games quickly and typically dont even finish the heart by the time its over. In longer games, it is harder to farm, but if you control dragon, and at least mid-ground for lanes, you can rake up gold for Sheen/Aegis/etc.