I am considering your advice, I will consider it for a new change on my build when I got some more time.
CounterSnipe, man, very nice commentary! I will try to use your advice in my games as Alistar and I will see!

1) Your masteries are misplaced. I find it's superior to run Alistar as a support given a 9/0/21 page, focusing on picking up all of the CDR from both the offensive and utility tree. This allows Alistar to have 10% CDR at level 1, which is huge.

2) Your items (starting) - The problem with your starting items is that you don't include a pink ward. You must always get a pink ward in order to counter ward the enemy lane. You can use your pink ward to
1 - remove enemy vision from the river and allow your jungler to lvl 2 gank
2 - remove an enemy ward from your bushes so you can hid in them effectively.

As for your other items, I don't agree with some of the build choices. Considering you got philosopher's stone early, as you should, you don't upgrade it until late game. Having the upgrade at about the 20 minute mark is when you want it, not the late game. The reason for this is due to the fact that your lane should be breaking down at this time, meaning you can roam. This increases your ability to gank, and your ability to help your team run away if you need it.

Finally, having ghost on Alistar isn't needed. Consider Alistar is currently the CC king of LoL. With this said you should be using Exhaust instead as this will only further enhance your already OP CC. Another consideration would be Ignite, but that's only for kill lane.

I think you should play some more alistar games and consider what Ive said. I'm not trying to discourage you, I just think that you have some misconceptions about Alistar which need to be addressed if you want to play him better. I didn't down vote, I didn't up vote.

Oh, also, you might want to take a Master point out somewhere to put it into Summoner's Wrath if you take Ghost, Ignite or Exhaust (I take it because I use Exhaust).

Between Shurelya's Battlesong, Athene's Unholy Grail, Randuin's Omen and Spirit Visage, you exceed the CDR limit by 5% without taking into account the masteries. Between a Frozen Heart and Shurelya's Battlesong, you max out CDR anyway, so you can take other support items.

Spirit Visage doesn't really increase his heal that much, since he doesn't have much to begin with and then even with Athene's Unholy Grail, he has 180 + 0.2AP = 198

198 + (15% for Spirit Visage) = 219.70 heal.

So you heal for 220hp each time at maximum, which is not really worth it, imo. The heal is for pushing lanes, procing your passive against turrets... Unless you're playing AP Alistar, your heal isn't worth very much.

The AP helps your passive, Q and W as well, but support Alistar isn't taken for damage, but because of his CC. So there's no real need to maximise his damage output. You're playing support Alistar, not AP Alistar.

As for mana problems, they're solved by Philosopher's Stone/ Shurelya's Battlesong and Frozen Heart.

I only suggested the change on Force of Nature because the item is getting removed and its various abilities redistributed to other items. Also that Force of Nature isn't usually taken on support Alistar. If you're thinking about mana problems, a Banshee's Veil could work as well, instead of Abyssal Mask as I suggested before.

If it's anti-healing effects you want, you could try taking a Kage's Lucky Pick and turning it into Morello's Evil Tome. I don't really recommend it, but it's just a suggestion. Because I really don't like Ignite on supports. Exhaust is much more useful and Ignite should be taken by your carry. Exhaust prevents the target from maximising their AA damage.

To be honest, you can work around your team as well, most of the time. For example, if you have an Amumu jungle on your team, you can almost guarantee that he'll take Abyssal Mask, so you won't have to yourself, Skarner may take Frozen Heart himself, Galio may take Abyssal Mask, Nocturne may take Aegis of the Legion and so on, so forth.

I also recommend a Zeke's Herald as a situational item. When your laning partner is Draven, Kog'Maw or Miss Fortune, for example.

I don't really have to say anything..... Just look at it.... fyi u left 0 spots for endgame wards

I agreed and changed some things, but if i did all the changes you're suggesting there, the guide shouldn't exist since it would be just another Alistar guide.
I think that is an ideal item for Alistar, eventhought when it's not meant to be built by supports, it gives Alistar all the mana sustain he needs, CDR and Magic Resistance.
I think is a good option sice it enhances the healing, and it gives you some more health, anyways I agree with you in the point that is a better option to be in the main build.
I deleted but I kept
can be used for every champion for avoid healing, anyways I don't recommend an Alistar player to use it if he's not sure if he will play against a healer, or there's more than one in the team yet.
I also activated the option you said.
Thanks for the criticism!

You might want to turn 'comment to vote' on.

Wow. Where to start...?

No GP10 Masteries? Awareness unnecessary, Strength of Spirit unnecessary.

Ghost, Flash and Mobility Boots? No need for all that. Swap out Ghost or Flash for Exhaust.

Soul Shroud isn't that useful. Neither is Spirit Visage. Athene's Unholy Grail isn't really a support item... In your main build, swap out Spirit Visage for Aegis of the Legion, Force of Nature for Frozen Heart and Athene's Unholy Grail for Abyssal Mask.

If you're going with Greater Mark of Magic Penetration, you should probably max Pulverise first. Since your heal doesn't do that much anyway.

No real need for Ignite on Alistar as well.