I agree with everything he has said. I would add in though that your build lacks some form of damage. Your CC alone is not enough to warrant people attacking you. As the tank, you need to be targeted so that the opponents don't completely ignore you and go for your allies.

Your CC is brutal and you can disable your opponents, and heal your allies, but I feel after you use your CC this build can do nothing useful in team fights, which is what Alistar shines in if built properly. At the very least I would try and work in a Sheen, or some form of AP dmg. For instance Kage's Lucky Pick is a good grab for its gold per 5 and AP boost, or a Dorans Ring, giving you health, mana regen, and AP boost.

see earlier comment as to why down vote

Can't see anything seriously wrong with your build but I think flash is more useful than teleport. Flash just works so well with alistar's headbutt and pulverize.

I can't really see the use of teleport over flash. Teleport is just not very strong compared to the combo flash pulverize, headbutt enemy into your team and ult the damage from their team as you stroll back towards your team and pick up another assist. If any high value target on their team is slightly out of position you can punish them massively for it. You say "get back to the lane extremely quick" but for what reason? Your AD carry is farming minions and you don't really need the slight experience gain teleport gives you.

I think you undervalue cooldown reduction. CDR = more ults, more CC, more heals, less dmg taken(due to cc), and Pulverizing mutiple enemies twice in a team fight instead of once is game changing. You lose some survivability from gear but gain it back from added CC. People shouldn't be focusing you first anyways.

I am at the moment undecided on my vote, (I will vote when i make up my mind/if you make changes then PM me and i will vote up almost guaranteed). First, like the first comment you need some formatting and BBcodeing use the link he gave you, its one i always recommend. Second, I disagree heavly with your skill sequence order, now i realize your going more support Alistar but in reality your heal on 1 person is not that noticeable (though its aoe effect heals for more total then most supports do now). This means that the insane ammount of cc you bring to the table is much higher priority (aka max Headbutt first then Triumphant Roar). You control the lane with your cc and pick someone off and isolate them for your carry, your carry will get fed. Also the damage on Headbutt scales very well early so you need to maximize your damage out put here because you will be less deadly damage wise late game(you can use Headbutt to keep enemies off your carry and do enough damage to make them think twice).

All in all pretty standard build, and again i see your going support Alistar im just not sure about your version of it yet. keep it up, add some formatting and you will be good to go i think.

+1 rep if it helped.

I'm not going to vote, because this is a decent guide generally, but lacks formatting.
Look at this: http://www.mobafire.com/league-of-legends/build/making-a-guide-101506?subscribe#chapter1
This will make your guide a lot better.