I made this build because I didn't find any builds with my favorite Item on Alistar, the Ardent Censer. It's some extra attackspeed for your allies, so I love it. Got a Tristana with 2.5 Attackspeed with all things :D

Strong defence is important, because Alistar is a tank. The extra life and armor will help you with your ult in the Teamfights. Movement Quints will help you saving your adc with a W or to land your Q. the Penetration is to deal more damage on other tanks and the Hybrid Penetration is for your abilities. YEah they're doing damage too

My opinion. Do what you want

Ardent Censer boosts the attckspeed of healed or protected allies and is the perfect item for Alistar. just use your E or a shield-item and the adc deals much more damage. It also offers 30 magical damage per hit. Per hit! and don't forget the attackspeed! A pretty dangerous cmobination :)

You're the sup. So you ward the river and help your adc at farming. lastht the cannon-minions and some melee-minions when your startitem is ready. Its very important you get the cannon-minions! For dummies: You AND your adc get the gold for them if you use relic shield. If the enemies get to close just use or W to get rid of them OR...

you rek them. The easiest combo is (Flash if you want :P)-Q-[walk behind them]-W(In the tower xD) and if needed then E,R or the Items. If you land that, it's the turn of your adc. you just do some autoattacks. You can also W to them and right after you ht them Q so they're in the air and not 500 miles away. This needs some practice but it can be useful. In Teamfights you go in (with your W) use R-Q-(W if you don't used it to kick someone away or to your team)(E) and just autoattack with your shield-items to tank the damage. Be sure that your team is ready to fight!

+ You help your team with the extra attackspeed and damage

+ Many shields and heals to save them

+ You can destroy Teams by kicking the enemys in better spots ;)

- You are not THE tank

- You have to use the Items in the right time on the right Champion

Thank you for reading! Remember: This is just a guide, not a law. Do what fits to your playstyle ;)