In an article for For Dummies, “Kupe” Kupersmith, Paul Mulvey, and Kate McGoey provide some basic information to absorb about business cases. For instance, they discuss the different purposes the business case can serve. They of course articulate the viability of a given solution, but they can also be used to support a feasibility study or even to prioritize projects.
The authors have tips about how to design a business case as well. If the person who will review it is already familiar with the issue at hand, you should not feel the need to get into minute detail with background information. The opposite is true as well. For many more tips about how to write a business case that resonates with your intended audience, you can view the full article here: http://www.dummies.com/how-to/content/how-to-write-a-business-case-as-an-analyst.html