Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
Renekton 3v3 build can be played in 5v5 as well :) This build has made me an unstoppable monster which would rarely die and if I did die well there comes guardian angel and... Reborn! He is a pretty overpowered champion because he has stun a lot of dmg can save him self easily and can beat the enemy team till their bodies hit the ground! XD
For your items you will have to get a doran's blade for the first blood and sell it when you are about to make the last item