ive been playing Ren since he came out and i must say that i really like this champ. that being said there is some things that he lacks. i was building him as an off tank, but found that to be kind of useless. so i was looking around different builds and i thought what does he need, CdR, Armor pen and some defense so he can survive in team fights, and this is the build that ive came up with.

for runes ive tried many different varieties and i feel that these really compliment him well.

for marks i go armor pen, seals armor per level (though im still buying thses so im using flat armor at the moment), glyphs are magic resist per level and quints are movement speed.

now these are what i use, they are not set in stone, use what u have, but armor pen marks are a must, end of story!

i feel like with the rune combination and having a 9/21/0 mastery set is all the defense ren needs, allowing you to get the damage that he needs to be useful. again, this is what i use and what i like, if you feel like you need a full offense tree go ahead, i dont recommend it though

exhaust is a must, and i feel that ignite will help you early game get some kills/assist so you can build your items, i was using exhaust and ghost but with the movement speed quints and ghost blade i feel that i could go some where else with one of my spells. again, this i what i use and what works for me, use what you think is good, no wrong answers.

dorans shield and health pot for staying in lane and farming up, after that i get boots and brute, then i get a vamperic scepter and heart of gold and avarice blade for the gold regen, next item is black cleaver, damage, armor pen and attack speed, works great, then i go ghostblade then starks and then randuins omen, then elixirs when build is complete.