A monograph, which is a book-length scholarly work by a single author, is normally expected to focus on some specific thematic or theoretical area within a sub-discipline and make an original contribution to research in that area. Cultural studies is an extremely diverse filed, which can encompass studies of race, class, gender, and ideology. Although cultural studies methods can be applied to many phenomena, many of the most important works in the field examine how forms of cultural identity and i8deology affect popular culture. Thus a good starting point would be to examine some specific theme in popular culture that interests you. That could include some element of material culture (clothing, food, furniture, etc.), internet culture (video games, blogs), popular music, etc.