Gnar Build

I went pretty good as bruiser on pbe, meaningfull dps in miniform, quite the frontline in mega-gnarl form, and impressiv burst. Went brutalizer->vamp_>trinity->randuins->BC->banshies->hydra with cdr boots somewhere in between hydra is great for aoe burst in mega form, but could be replaced by BotrK for better dueling and dps in miniform

I can't say I've played him enough to be certain, but he does very well riding on his kit damage alone and built tanky. That being said he scales obnoxiously well with even a little attack speed. Building Zephyr seems to be a very good option so far, tenacity/MS works alright with his mega form and the extra attack speed gets his aa augment in mini-form up a few notches. Personally, item wise I think he has a good parallel with Shyvana. Tanky works fairly well, but a little attack speed to profit off of her %health shred works very well too.

As far as playstyle he's a tank frontliner with the option of decent poke too, and while this may sound OP the fact that his capability to be the frontliner in question is so very predictable takes a lot of the abusability out of it.