I have seen vertical, horizontal and "T" shaped windows. I think the vertical windows work really well. I have seen round, square, octogan, pentagon and some other shapes on bow blinds. I like the ones that are partially buried and rounded on top just hard to keep the water proof. I bought and put up a Midwest Haybale blind this year and really like it for ground hunting. I had one small window in the front that was 8" wide and about 16" tall.(you can put windows where you want and what size you want them) I would think if you can buy a couple of cattle panels(16' long) and have a base welded out of angle iron to attach the panels on in a haybale round shape it will make a great blind. You can cover in a black tarp or plastic then put hay or straw on the outside to make it look like a haybale blind. Won't want to do it with cattle though. I am going to build a larger verison of the haybale blind I bought this year.