Question: How to choose your box and cut out main frame.
Options:
Find a box and cut around where there are plenty of creases.  Make a square cut out as big as you would like.
Find a box and cut around where there are no creases.  Make a square cut out as big as you would like.
Answer: Find a box and cut around where there are no creases.  Make a square cut out as big as you would like.