For me just a one hunter blind I have found 5'x5' being best and 4'x5' being second best. I start with standard 2"x4" cut them equal width. I cut the roof supports and wall supports 6.5' tall at the shallow end and 7' at the tall end. Not a lot of wasted space to heat that way. I heat with a Colman back pack stove.I made sure I can still use the ram rod in my muzzle loader before I chose that size.
I use 3x1/4 inch lag bolts to hold the frame together and 4x1/4 inch to hold the frame to the floor.
All the bracing is done with 3 inch wood screws. Hope you can get the idea from these pictures.
Window framing in this picture. door framing is similar.
I covered the out side of this one with some corrugated fast food restaurant road sign. then covered it with recycled siding roofing steel. Most I just use the 1/2" 4x8 OSB and OOPs stain from Home Depot.
Roof is recycled steel I sprayed with expanding foam, Is OK but better to lay the steel on a sheet of OSB with a inch air gap to keep noise down.
This is a 4x4, it works and is warmed easy but a bit cramped when trying to use a longer rifle than my 870 slugger. It is some cheap T 1-11 I got.
I pickup carpeting along side the road, Always lay it out on the drive way and spray it down with soapy water and use a barn broom on it to kill any beg bugs or fleas that may be in it.
I never pass up a window setting along side the road. Not mater the size if it isn't tempered you can cut it to a useable size with a cheap glass cutter.
Window frame is cut down 1x4 to 2"wide. A 1/8 inch grove down the center of what is going to be the inside to hold the pane of glass. In this case the pane is from one of those windows withal the panes and bars. Two of the panes come together leaveing a seem in the center. You can hone the glas with a whet stone to make them fit real tight.
I hinge mine to fold up on the inside and use the eye and hook to hold them up. It snows, freezing rain and such here so having sliding windows will many time give you a window that won't open or shut even.
I have also used pallets to screw to the frame to close a blind in. I make them modular that way I can put them up on the stands alone and use the lag bolts to hold every thing in place.
I fully recommend a square to square the whole frame up on the stand and square the window frames.
Hope this helps.
Al