I don't think you want to be using styrene! You'd get better results with motor oil. ( I'm not kidding about the motor oil.)
EDIT: Oops, I thought you meant surf wax! BIG, BIG, difference, eh? The motor oil was the additive used by Wax Research, in their original purple surf wax. For those old enough to remember, it was actually pretty good stuff.
If your going to make surfacing agent, the wax ratio is about 5-10% wax to styrene. Just grate the wax into something and stick it in the styrene. At anything above around 65 the wax will emulsify into the styrene. The ratios don’t have to be exact, and a bit more styrene in the resin will make it flow, and cover more effectively. I could say more, but that’s the basics.
Oh, don’t be an idiot, and mix molten wax into the styrene, because that’s what an idiot would do.