Step 4: Gluing
Glue two 10,2x10,2cm pieces (square angled) to one 10,2x12cm piece.
Glue the 10,2x10,2cm piece with the 9cm hole in the middle between the two other 10,2x10,2cm pieces approximately 3cm from one side.
Glue the last 10,2x12cm piece on top of the 10,2x10,2cm pieces.
Glue the two 3cm pieces into the 12cm holes of the 10,2x12cm piece.