The design of your study will be guided by a number of factors including:

• The literature you reviewed, you will more than likely use similar studies conducted as models of how to conduct yours.
• The limitations imposed by this setting, i.e. you have about a month to carry out your study, and you are limited in resources (it is unlikely, at this point in time, that you can conduct a true experiment, for example).
• Conversations with your instructor, there are variations across courses in how instructors expect the study to be conducted. For example, some will want you to use only university students or psychology students, other expect you to go outside of the campus to recruit participants.

Therefore, the best advice is to pay attention in class because that is where you will get information about the rules specific to you, and the reason for the limitations imposed by each instructor.

By the way, the description of your study, i.e. the 'design' will be described in your procedures section, in within the methods section of your paper. It may help for you to review some procedures sections in the articles you've read to see how detailed they are. Remember, your description of the design should be detailed enough that someone can replicate your study.