When you know you need a business case, you may want to begin looking for business benefits and costs immediately. However, that is the first step on the road to meaningless results. Business benefits exist only by design.
Costs and benefits exist only by design!
Reaching objectives has value. Business Benefits and Costs are best defined in terms of business objectives.
That isn't always what people in a hurry want to hear. Sometimes there's a real sense of urgency. The financial justification or the ROI really does have to be complete yesterday or else heads will roll. Never mind the academic niceties: this thing has to get done!"
I receive calls from business people in this frame of mind. They start by explaining they are building a business case for this or that proposal, or decision. Invariably they ask immediately
Which benefits should I include?
Which costs belong in the case?