There are many formats for business cases. Emrah Yayici of the consultancy BA-Works suggests this template:

• Business requirements (why is this ERP solution needed)
• Scope - the definition and prioritization of features needed
• Context - the application landscape the ERP system operates within
• Cost vs. benefit analysis - for product/project feasibility
• Risks - identifying and mitigating product/project risks

You could do worse than adopt this template for your ERP project at the start of the selection phase.

Selection 6