I scored six of these Anderson wood frame double paned windows for $10 each at a salvage yard.
They are of the same "genus" as the living room windows. Very convenient.
Snapping a chalk line for the new window rough opening.
I drilled holes through the plywood from the inside after I had determined the
exact corner locations. Pushing nails in to the holes from the outside allowed
us to set up the chalk line "blind".
Cutting the "shack" new window rough opening.