First I had to measure the space that it was going to fit in so I needed to make sure I had the edges the right length, three of which I had in the picture here.
Step 1: Designing the interior
Once you've got the frame, you'll need to be aware of the length of the inner sides so that the interior parts will fit. E.g. the height of the unit is 92cm but with the horizontal pieces attached, the inside length vertically is 88cm.
Some of the pieces of wood were in bad condition with pieces broken off so I just painted them white to hide this as much as I could.