Assemble Framing

Place vertical studs (60-5/8") inside horizontal top and bottom plates (48-3/4")

Sandwich plywood strip between two of the three 33" pieces and screw together (three screws across length is fine)

Use sandwich to form top of window box, use 3' members to form sides and remaining 2'9" member for the base; screw together with 3-1/8" screws (toe-in screws at a diagonal into top plate from side members) - IMPORTANT Window hole must be at least 3'tall by 30" wide

Screw one stud (60-5/8") to either side of window box; letting top of studs hang free off the top of the window box but making sure they are all aligned at the bottom

Toe-in center vertical above window box

Place top and bottom plate such that vertical studs at edges leave a gap of 7" to one side of window, and 2-3/4" on the other.