I usually build renek to be a bursty phys hero. First item is doran shield, that + your cull will keep you in the lane for a very long time. Next I pick up boots + sheen and after I finish whichever upgraded boots I need I work towards a bf sword which gets turned into a black cleaver. From there pick up a defensive item, whichever the game dictates, and finish off your tri-force.
11/19/0 is the way I go for masteries. Picking up both attack speed talents in each tree, and the arpen in offensive.
runes = arpen marks + quints, armor yellows, cdr blues.
this leaves you with high burst, reasonably sustainable auto attacks, mobility, survivability, and very good early-mid game arpen.
The good thing about Renek though is there's more than a couple sucessful ways to build him, this is just one. It all depends on your playstyle. He can be built very tanky too.