The (standard) format of a thesis is 170mm by 240mm. The complete cover (front, back, spine) and bookmark / invitation are printed on a sheet of 450mm by 320mm. For trimming you should reserve a 3mm margin.
I used the Arches cover paper for the cover of our book in a workshop. It takes all kind of media. We used goauche, colored pencil, and watercolor.
In order to build the cover file:
The cover letter should include your name, the title of the research paper, the date when the paper was assigned and the date when it was turned in, the name of the instructor, the name and the title of the class, the section and the homeroom. The format used in cover pages is usually MLA, although the professor's requirements may differ. Also make sure you clear out all the details, for some constituent parts and details may be mandatory.