How big you make your arena depends on your financing (bigger = more expensive), the space you have to build it on, and what you want to do with it.
Ideally, if I could have any size area and money/space wasn't an issue, I would have an arena big enough to put in a standard size barrel pattern, with pole bending beside it (so you don't have to take things down and set them up). So I'd want 150 feet x 220 feet. ***in a fake world, anyway***
∞•*˚ Βгįťţαňγ ˚*•∞
It is not enough to know how to ride; one must know how to fall.