This came together very quickly using a four (4) Sleeves from the Artfully Sent. Pages 11, 43 and 46. Slice off the back piece and adhere together.
Cut two square bottom pieces. Add one from the inside and one underneath. This will provide better stability once assembled.
Before starting the assembly of all four (4) flaps, you'll need to cut four (4) pieces of vellum. Adhere the velum from the inside then start piecing them together.