Don't itemize just for dragon/baron control, because you'll think you're doing it sneaky, having warded and dewarded around drake and doing it solo jungler, but if the enemy team/jungler guesses it your itemisation won't help much in a smite fight.

Nunu can solo drake from lvl 6 onwards, if you're willing to use your ult to get some of that huge dmg that would be too long to do over time, because E is not so good as a damaging spell (cooldownwise, else it's a good spell in a burst combo). His Q is of course very good, but the CD is way too long, and I'd suggest you keep it for doublesmiting Drake or Baron.

I'd never solo Baron as Nunu, even in a bot game when you're super fed, because that's something only AD hypercarries can do, like Master Yi and ADs with insane sustain. Duo Baron with hypercarry like Vayne can work very well because Nunu tanks well and can boost AS. It should work any time from mid game onwards if you or your carry aren't so far behind. But always keep in mind that the presence/absence of the ADC and his last seen position is the more important information for the enemy team.

Do a AP/tanky build, get Spirit of the Spectral Wraith early. The equilibrium between AP and tanky will depend on enemy team comp and yours, if you lack APCs, get some AP and play sneakier to get those ult traps that can turn games at lower elos. I'd personnally get mega tanky items that allow me to reach the 40% CDR cap that's very important to keep your carry on steroids and perma-slow an enemy. That and of course, great sustain and Q buffs easily, and ult available every fight or so.

Don't itemize just for dragon/baron control, because you'll think you're doing it sneaky, having warded and dewarded around drake and doing it solo jungler, but if the enemy team/jungler guesses it your itemisation won't help much in a smite fight.

Nunu can solo drake from lvl 6 onwards, if you're willing to use your ult to get some of that huge dmg that would be too long to do over time, because E is not so good as a damaging spell (cooldownwise, else it's a good spell in a burst combo). His Q is of course very good, but the CD is way too long, and I'd suggest you keep it for doublesmiting Drake or Baron.

I'd never solo Baron as Nunu, even in a bot game when you're super fed, because that's something only AD hypercarries can do, like Master Yi and ADs with insane sustain. Duo Baron with hypercarry like Vayne can work very well because Nunu tanks well and can boost AS. It should work any time from mid game onwards if you or your carry aren't so far behind. But always keep in mind that the presence/absence of the ADC and his last seen position are the more important pieces of information for the enemy team.

Do a AP/tanky build, get Spirit of the Spectral Wraith early. The equilibrium between AP and tanky will depend on enemy team comp and yours, if you lack APCs, get some AP and play sneakier to get those ult traps that can turn games at lower elos. I'd personnally get mega tanky items that allow me to reach the 40% CDR cap that's very important to keep your carry on steroids and perma-slow an enemy. That and of course, great sustain and Q buffs easily, and ult available every fight or so.