Anyone got some good tips for Alistar building/playing?
I figure that it's good to start with RoA after Doran's Shield and boots (cooldown ones), but I never feel tanky enough and I get harassed down really easily.
You're not tanky enough because you're trying to play AP Alistar. Every time I play against an AP Alistar he just gets melted, ult or not. And then when I mock the enemy team saying they have no tank, they reply "rofl idiot alistar is tank" and really, he isn't when he has RoA, AA Staff, lich bane, deathcap, doran's ring (depending on how far the game is going), and sorc boots. Sure has CC and a decent burst, and a spammable AoE heal, but it really doesn't make up for what a support/tank/ad Alistar can do.
If you build a tanky/support/AD Alistar like me, you have the CC, not-as-good-but-still-decent bursting, great tanking, and some nice auras. Even early game when you have 1-2 gp/10 items and boots of mobility, you can ward everywhere you need to on the map and still make it back to bottom lane before anything big happens.
Never follow the same build pattern every game, but this is usually what I build on Alistar.
HP Regen -> Philo Stone
Boots -> Mobility
WARDS WARDS WARDS
Winning really really badly?: Sheen + Phage -> Trinity Force (if you can afford it, good luck this early), and if you really can, MORE WARDS
Equal grounds?: ruby + cloth armor -> Aegis of Legion + MORE WARDS
Not doing so well?: Heart of Gold + MORE WARDS
If you got Trinity Force built, well done, get Aegis if you don't already have it.
If you don't have it yet, and you were trying to build it, and things seem to be going not as good as before, get Aegis if you don't have it yet.
If you have Aegis, get Sheen if you don't have it or trinity force. With your ult and base damage alone, sheen will go great with your headbutt. You can auto attack during a headbutt. This pretty much makes headbutt apply on-hit affects like Parley and Urchin Strike, on top of it's very useful knockback.
If your team is still not doing too well and you already have aegis and sheen, get warden's or a negatron cloak depending on which is hurting you more between PD and MD. Always look at death recaps. They tell you what's hurting you the most between 3 sources of damage from 3 enemies. If wardens or negatron cloak isn't good enough to stop that PD or MD you're taking, build them further. Warden's into randuin's, Negatron into Quicksilver Sash. Keep in mind that both of these items have actives, and you'll want to move them into the 1-3 slots. Good players know Alistar's ult removes all current CC on him, and they will usually try to bait you into using it before you need it in a teamfight. Quicksilver sash allows you to have two CC cures without needing to give up one of your summoner's for cleanse. If you're just removing CC, use sash first. It has a shorter cooldown.
Once everything's complete, you'll likely have: reverie (whenever you feel you need it after philo stone), omen, sash, trinity force, aegis, and any boots you prefer for lategame.
Of course, you don't absolutely need reverie, omen, and sash. Replace them with whatever you feel you need most, but just be sure you're replacing omen with armor, sash with magic resist, and reverie with another support item or even warmogs if you swing that way, or even an empty space for MORE WARDS. Just make sure you're keeping trinity force and aegis of legion. Replace boots once you feel the movespeed isn't needed anymore.
People don't seem to realize the potential with trinity force on Alistar. His ult gives him a flat AD buff (+60/75/90). Trinity force will scale this (x2.5, aka +150/187.5/225) without needing to smack them multiple times (Attack speed, which it gives anyways). It also gives crit for that chance of scaling it even more. You're tanky, supporty, a heavy CC dealer, and can still burst their squishies with ease.
Now what would you rather have? A super hybrid of a Tank/Support/AD, or just a squishy melee Veigar who isn't benefiting from the AD of his ult?
Also, don't get Doran's Shield.