What would your build for nunu top be
Okay so first off I don't recommend playing Nunu top against tanks. Nunu's snowball and ult can do a lot, but not against someone with MR.
I also wouldn't use Nunu top against a top laner or a jungler who have hard cc like stuns, silences, knock ups or fears by level 6, because most of your damage output comes from your ult, which is pretty easy to interupt. If you see a xin zhao, or a fiddlesticks, stay away from nunu.
I only played him because I thought I would go up against a Jayce or a Kayle and both are squishy. Over a series of trades, the sustain from Nunu's passive and his feed will put him ahead, which will give him a huge advantage over mana dependent lane bullies like Jayce and Kayle.
Xin Zhao, Fiora, and Lee Sin are also squishy but are more all in oriented. In this case, you'll have to wait for them to use up their hard cc before you ult otherwise they'll interrupt your channel or make themselves invulnerable before they take damage.
Nunu is strong in lane because of both his snowballs and his sustain, but at level 1 you don't get both, so I started flask and pots to substitute for any mana and health I lost at level 1 and to prevent my opponent from forcing me out of lane. Kayle has a lot of lane pressure at level 1, and jayce has both poke and all in potential and a full rotation by him at level 1 hurts like a motherfucker and will pretty much guarantee him the early level 2 which could put you at risk of giving away first blood.
I bought hextech revolver to make my sustain that much stronger, and it got to the point that between the sustain and the damage from my snowball and ult, I could only be killed by a three or four man gank, which is where those deaths came from. Top laners should always relish receiving that kind of pressure because it makes the rest of the map vulnerable, and your team can take dragon or towers at their leisure.
But getting killed is never optimal, if I had map awareness I could have drawn the enemy team to me without getting killed.
Remember not to be cocky when dealing with champs that can interrupt your ult's channel.
Once I got revolver I transitioned into DFG to make me a real threat in teamfights, since I don't have that many spells to go through to complete a rotation before I'm focused down (if I'm focused down) I can get a lot of damage out without much counter play.
I probably would have built tanky that game after DFG, just to help me survive long enough to channel a full ult, but the enemy team surrendered at that point.
Also, get boots and upgrade them somewhere in there.
it's important to remember that Kayle's ult should make it impossible for Nunu to kill her, since he only has two damage spells, I got first blood on her after six because she misplayed. My other kill was from fending off a gank from Wukong.