This is my first build and I made this for all those out there looking for a good Alisatr build. I have found Alistar is great as a 3v3 champion and haven't found a real nice build for him in a 5v5, I am in the process of this now. I also got to say don't stack your trample if you dont need to, if you do it will put out less damage but if you have to then do it.

For my items I went with armor and magic resist. His items can be very situational depending on who is on the other team. If you see a lot of AP being built on the other team don't focus on armor so much and switch to magic resist force of nature would be helpful here, and vice versa with ADget more armor and thornmail is always a good option. And if you are totally dominating the other team go for more items that give you AP while still doing armor and magic resist since it will help with your skills.

For Alistar get atleast one rank for each skill going pulverize, triumphant roar, then headbutt after that you decide what you need most at the time but always get your ultimate when available. Pulverize will get your stun, help gank or stop your team from getting killed. When you hit level two you'll be able to lane longer with your team since you are able to heal yourself and your team (minions and champions). Headbutt is a skill that you will have to be very careful with, it can get you a kill or assist or you could just end up helping the enemy get away. Try doing a pulverize before and go to the other side of the enemy champion and headbutt them towards your team and watch the enemys health melt away.

Pros:
-played the right way and your team will love you
-can lane a long time
-help your team lane a long time
-not very item dependent
-will help your team level
Cons:
-played wrong and team will hate you
-keeping you and your team with health will drain your mana so use triumphant roar wisely
-you will get lots of assists so you wont level as fast
-doesn't level all to fast (you might be two or three levels behind)

You are a support tank take hits and disrupt the enemy team, just dont get carried away because you won't get many kills alone. If you and someone else are chasing an enemy champion and you have your ultimate then tower dive and pick up a kill/assist. If you are at a point where you know you wont die by rushing and your team will be there momentarily to help you then take the initial burst of damage and watch as the other team doesn't have the skills they wished they had.

You will be in a lane a lot unless you see an opprotunity to help a different lane push back or help pick up a kill/assist. If you see someone tower hugging the turrent will most likely start going after you because trample hits units surrounding you, so back up and wait, go into the jungle, or the another lane.