i start off negatron cloak and 2 cloth armors most games but it matters if they only have 1 ap or the ap doesnt worry me much i may start off chain vest + cloth + t1 boots or 2 cloths + null -magic mentle + t1 boots but if you really want to be super tanky start off the negatron cloak + 2 clothes is the way with a health pot if you want to stay the tanky root and your team held top long enough for you to get 1100g then you can get gaint belt if not then get t1 boots right away even if your at 900g if the enemy has alot of ap get the mercury and spirit visage before the frozen heart and gaint belt if they are alot of ad get frozen heart or if you got the giant belt right away think about sunfire then get frozen heart if you notice your always running out of mana get the glacial shroud that will turn into FH unless they have like 4-5 ap and almost no ad damage upgrade negatron cloak to FoN last as far as your 6th item that i leave for you to choose but dont get it til you complete these 5 as far as runes the seals and glyphs are a must the marks and Q are what i perfer.

with the negatron + 2 cloth + health bot + your E heal + summoner spell heal you can take a pounding and heal yourself and your teammates exhaust is there to protect your teammates if you see 1 enemy going at a teammate and you have to stop the rest of the enemies with your Q and W you can use exhaust on that 1 enemy that got by you so hes shut down while you shut down the others. i play alistar as a tank for top in dominion but i will gank bot and if bot cant hold and the enemy is like a tank alstar can go bot and outbeat the tank by purely using
Q and E on the minion waves while using W when they come in close and try to attack your minions. you wont last forever but you should be able to push enough that by the time you recall and get back he has just gotten near your turret so you can start it over again.