Here is my very easy DIY toy bin storage using old nappy boxes.
1. To make the opening I first make an outline by using the top flaps as my guide. This will also make all my boxes have the same size opening.
2. Fold down one flap for the side outline
Do the same for the top using the other flap. Join the lines on both sides for where you want to cut. (Also these boxes have cutout handles already if you want to incorporate them into your toy bin)
3. Once you have cut out the opening sellotape or glue down the top