I have a very small woodchip which i can jump a single fence in it is slightly bigger then a 20metre circle(sorry dont know the exact sizing) it was originally built for me free jumping my youngsters.
However i have a big 20 jump course set out in the field which is to big as i forget sizing.
I would go with a size you feel happy enough with say like warmup arena size BUT build it so when you get more finances it can be enlarged further. This is what a friend of mine is doing granted hers is outdoor
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