Let me first refer you to two excellent web pages:
(and the equivalent jinmaku page here http://www.sengokudaimyo.com/miscellany/curtains.html)
I was planning on making a vertically striped akunoya, but I finally changed my mind for two reasons: the leader of our group thought it looked too much like circus tents, and, most of all, a vertically striped akunoya would imply much more sewing, which I won't really have time to do this summer.
So, I settled on this design:
I'm starting from this carport (hey, it's free, so, even if the shape is not perfect, it will be good enough for us this year!)
I was planning on making a whole new shell for it, but I can't locate suitable canvas locally and ordering it online would be costly. It's the first time we go there, we don't know if we're going to want to go again next year, and with the shape of this thing not being ideal for an akunoya, I'm not sure it's worth making a whole complete waterproof replacement cover for it just yet.
What I will do instead is buy cheap broadcloth and make a quick shell to go over the plastic. We'll be dry, and if the weather is nice we can raise the sides and just leave the fabric hang down. If we like it, next year I'll make a better one and reuse the fabric for garb :-)