I highly suggest identifying the data your decision-makers are using to make their project/program approval decisions. Who is making the decision and what criteria are they using? Then test the template and the content of your first few business cases on these decision-makers. Do they understand it? Did you provide them all of the information they needed? And when you get really good at this, use the business case process as a means to continually improve the project decision-making process.
Steve Romero, IT Governance Evangelist
http://community.ca.com/blogs/theitgovernanceevangelist/