I have been playing top with Diana and I like her a lot. I keep switching up my build right now and want to find something that works best for me.
I prefer to build her with health/armor early and then move into ability power.
I normally go ninja tabis, Rylai's Crystal Scepter, Frozen Heart,...and then I'm sort of lost as to what to get next and pretty much every game I end up getting different random things, hextech gunblade, rod of aegis, needlessly large rod, whatever looks good at the time. Ha.