He is in fact not strong as a solo top at all, and loses and becomes more useless as time goes on. There isn't a big difference between a Nunu with farm and a nunu support. His job is still the same, peel for the Carry, Blood boil your AD, and "E" the physical damage bruiser/carry who is trying to kill yours, or whoever is closest to your AD carry at the time. Nunu loses a lot of match ups top lane, and althoughhe has some safe lane match ups top with good sustain, he's not all that useful with farm like he would get in a top lane. You would rather want someone like an irelia or jax etc. However, of course he is a good champion and has the ability to win games at any level given the right circumstances. So if you enjoy playing Nunu solo top, play what you enjoy. Just know, it's very hard to carry or do much as a solo top nunu, compared to if you were to play a bruiser with insane snowball potential. (riven, jax, irelia, vlad, etc.)