I have these on a couple box blinds and really like them. I would highly recommend them.
http://www.gandermountain.com/modperl/product/details.cgi?i=400878 Mine are about 5 ft off the ground at the floor level. I used 6 ft 4"x4"'s I believe.
I would make them >4ft off the ground or so. One blind is 8'X8' one is 4'X6'. Treated plywood floors is a must based on what I have learned.
these windows make it very nice also.
http://deerviewwindows.com/hinge-window-3/ Lots of photos online about many different designs.
Good luck!