I'm a little confused as to how to build him too since resistances are totally worthless and nothing good really builds out of negatron anymore.
However, with season 3 I've started to build more damage and more health, fewer resistances. I typically go rush sunfire, then giants belt and negatron, build rylias and abysal out of those items, then maybe bulwark? I haven't gotten that far in any of my games.
machete 5, spirit stone most important on first back for sustain and to give mid blue buff boots & wards Then, if you fear a lot of ad, Giant belt -> upgrade spirit stone to the fist if you fear ap, maybe try bulwark
Other items to consider are cape, abyssal scepter, gauntlet, but games rarely run this long