First, this is very important, do NOT put a Zod in it. Everyone knows that gear loses no durability in PvP.
Start with a flawed sapphire to give it a nice blue color, then do 2 chipped rubies for decent fire damage.
I'd then put a Diamond(regular) for AR, since you will need a bit(about 200). The last slot should be used for a flawless emerald. Poison damage will be good.