I build them 4x4. I like a full size door and talll enough to stand up in and to put a shelf in up above the windows. Takes less material to build and like op said easy to see out and shoot out of all the windows.
We have several larger boxes on our place and they all turn into shelters for illegal aliens. They throw the chairs out and have fire rings built around all of them. If you put a lock on them they tear up the doors getting in them. Another reason for the 4×4 box blinds.
