Case studies usually require you to give a detailed analysis of the situation and to recommend possible future action or a new design. Your marker is looking for how well you analyse the situation and provide a realistic solution to the issues/problems.
Your marker would also look at the quality and reasonableness of your recommendations. Reasonableness includes that the recommendations could be achieved taking account of resources such as time and money. There are often many solutions to a problem but giving all possible solutions loses marks in a case study situation because it is considered unrealistic.
Your course description of the task should contain guidelines on the types of questions to ask when analysing the case along with other issues/possibilities to consider in your analysis and discussion.
For clear communication to the reader of your report, writing skills are very important. Your marker will expect clear and logical organisation of the case study report, cohesion across the whole report and evidence that gives credibility to your findings and recommendations.