"research design" case study "mixed method"
This is most important. Do not just google it, but also search your school's database for articles that have these terms.
When you find articles that had these 2 terms, you know that you will get a good example of the way to do case study research.
If you choose case study design, you can only focus on one case or a few cases. You'll have to analyze interview data and learn people's opinions. That is just one way to do it.
Then, add a new search term:
Outpatient Departments case study
See what other people have done and what they used for their research designs. You need to read several studies and understand them before you can write your own.
When you write the proposal, use the school's guidelines. Often, the proposal consists of chapter 1 introduction, chapter 2 lit. review, and chapter 3 methods.
Read at least 5 research articles by other health care researchers. That HAS to be the first step, and then you can learn from them and see what you prefer. It won't take long before you are a pro! So, read some articles and let's discuss their research designs.
:-)