For our projects we take the elements of a feasability report and put them inot the business case.
The outline is:
Situational Analysis(what is the business problem)
Objectives/High Level Requirements
Alternatives analysis (what are the possible solutions)
Recommended solution
Costs(project and ongoing, internal and external)
Benefits(tangible/measureable, intangible, additional)
Cost Benefit analysis(is there a reasonable payback in months or ROI)
Risk Analysis
Proposed Team Structure
Proposed Schedule
Issues
Final recommendation
Hope that helps.
James