Good business cases have some core elements in common. Gerald Hanks explains in an article for Chron. A solid business case template begins with an executive summary. This is a highlight reel that touches upon all the major points made elsewhere in the case. Although the executive summary should go first in the business case, it should be written last, in order to account for additional data that might be included along the way.
Beyond that, you need a project description, a schedule with estimated costs, and a cost-benefit analysis. The cost-benefit analysis is where you attempt to prove that the project will produce better results for the business than the status quo, and that the proposed project is better than any available alternatives.
For more, you can view the full article here: http://smallbusiness.chron.com/write-business-case-template-67054.html