Consider uploading hand sketches or a quick study model of all your first ideas. You can scan these drawings or take photos of your model.
Brainstorming ideas is your first step towards making an informed decision to the design solution. Learn more about that here.
AutoCad is a good way of brainstorming your ideas. I would love to see more of your ideas for your cafeteria! i also like how you want to give a section for students to study, I too, wanted to incorporate that idea in my brainstorming.