Anything you want-but for me when I costume design, I like to draw it traditionally-you can take a picture of the drawings and hand them in. I can also help you with the process if you want, cuz I've done it multiple times now.
So after that you're going to want to make a production metaphor-this is basically a thesis discussing what you think the theme of the show is-you're going to want to tie in visual elements. For example, here's one I did for Romeo and Juliet-
"Romeo and Juliet's warring families show us the ultimate uselessness of needless violence. That the family's war ends in the death of many of their loved ones shows that their hate was ultimately harmful to them both. This goes further with the unexplainedness of the family's fued, showing that the hate did not even have a real or good reason behind it. For this reason, Romeo and Juliet summons the image of a house of cards-it's foundations are unstable, and ultimately it will collapse under it's own weight."
Obviously it doesn't need to be this complicated, just something along those lines. From there you'll want to find a visual metaphor-a picture you feel sums up your production metaphor-here was mine for Romeo and Juliet-
