I added some built-in spacers because I thought that would be easier that buying some. This also means you don't have to have screws for the bottom, which allows the case to lay flat on the desk without needing feet. It might be a little bit higher than with spacers, but this could easily be changed.
The author remixed this model.
Where the holes for the spaces/screws on the bottom are, I added some columns to act as spacers.