Welcome to my AD Top Alistar build, this is an incredibily fun build and most will think I am just trolling. Partially you're right because it breaks the meta, and counters strong split pushing melee carries such as Jax and Trynamere to some extend. This guide is not intended for beginners and requires that people know the mechanics of this champion and the game to fulfill this build to its full potential.

Keep in mind that YOU ARE NOT A TANK! Having a proper initiating tank is crucial for your success.

Pros:

Good exchanges with Headbutt+Sheen
Huge Damage Spike with Trinity Force
Can reach enemy Carries easily
Peel and is a good Anti-Assassin in team fights
Extremely strong late game with Tons of Damage, Free Tankyness and Utility
Great 1v1 AND team fighting

Cons:

Weak Early Game
Requires levels before becoming good in lane
Low Mana/High Cooldowns
Beware the haters if you do bad

My item choices are melee carry style choices. I strongly reccomend Sheen as fast as possible to help win exchanges, while you push. Check out the "Unique skills" category for more details on why Sheen is so important.

The major purchase I suggest are Trinity Force and Ravenous hydra, because Hydra allows you to split push and farm faster (without using Q and its high mana cost) and Trinity force gives you every stat you need. Movespeed on Trinity is an incredibly important stat since Alistar has poor movespeed and allows him to approach enemies with his classic Headbutt+Pulverize Combo.

Not much to say, some people may opt for defensive bruiser build, but I think your ultimate covers all the defensive aspects you need. With a 21 offense build, you can last hit easily (last hitting kinda sucks with alistar), while 9 Utility, I specifically get the movespeed out of combat and mana regeneration so alistar can roam/return to lane faster and sustain himself easier. Biscuit is just a nice bonus! :)

Headbutt is primary source of harassment, as when they fly back they cannot properly engage back. It gives the most damage/lvl as well, but I suggest getting pulverize first ALWAYS incase your team wants to invade. It also starts at 60 damage while headbutt starts at 55 damage.

I've recently done this in ranked play, my winrate with Alistar is slowly rising (it sucked because I played him support before). I've also got a penta with him.

I play him in local tournamets and actually got Alistar banned before.

I strongly recommend you mastery alistar before playing him in ranked, or else you will end up a fool.

Below is a video Play Video

Wauto's (W+Auto Attack)

Takes timing, when you are about to headbutt an enemy, you MUST Manually RIGHT CLICK the enemy
and you will simulatenously deal Headbutt damage plus Basic attack damage.

Wauto's and Sheen

Using Wauto, you deal about 120-200 bonus physical damage in conjunction with your headbutt, this is the MAIN IMPORTANCE FOR SHEEN. Master This.

Pacing Sheen Proc's

Sheen has an internal cooldown of 2 seconds, so that means you should cast easy of your skills 2 seconds apart to maximise damage. This is common knowledge.

W+Q

Before your headbutt connects/just as it connects; you activate Pulverize [Q], effectively allowing you to close the distance and lock up an important target. Another valuable technique to master or ELSE you will headbutt priority targets AWAY and potentially allow them to survive

This basically the reason AD alistar works, at lvl 3 ultimate you gain 90AD and 70% damage reduction, so you can basically 1v1 anybody late game and works in your favour as a pseudo-tank in team fights. It is basically like Tryndamere's ultimate in function. MAKE SURE you use your ultimate at the right time, if your ultimate is down you are pretty squishy!