The only problem with Renekton jungle is that he is really hard to play, you need always to use he's abilities to stay him alive, but if you can do that, then he is amazing.
All these items are possible, it all depends on the enemy, but the core items is Cinderhulk and Hydra.
GA is EXTREMELY good on Renekton if you are fed, cause then when it poppes then you get 30% hp back and then you hopefully still have ultimate, so you on 1-2 secs get up on 1500-2000 hp, and cause of GA, i have turned around many team fights.