Notes from author
Just started building this one, it should be finished at the end of this week (16th of February 2014), but here are some notes and guidelines I've deduced from my invasion variant.
In the arena you want a reliable shield to block with in case you need to stall out the last 30 or so seconds at low health, the Grass Crest Shield just won't do, and the Heater Shield is recommended for its light weight / reliable stability / 100% Physical reduction / 70% Fire reduction.
Even so, dodging is still essential for this build's survivability. So the DWGR is definitely recommended.
People play differently in the Arena than in Invasions and one of the differences I've picked up on is that Power Within is completely useless in the arena. It conditions the opponent to play very defensively is more to your determent than your opponents. I'd definitely recommend 12 points in Faith for the Heal spell with the Thorlund Talisman for an extra 660 HP heal at the end of every kill.
The new Equip Load is balanced out with the Elite Knight Gauntlets for a bit of extra defense.
In case you're in need of some quick kills you can menu-switch the Dark Woodgrain Ring for the Hornet Ring and the Uchigatana for a Crystal Rapier +4 or +5, although I would not recommend relying on it because you're going to wear out your Rapiers quick, and if you're facing a Dark Sorcerer then you have to consider the the i-frames and lag in which case you need to stick with the DWGR!
Otherwise the principles are the same as with the Greysteel Warden invader build.
I can't wait to finish this build!