First of all there is no "Right" or "Wrong" approach:)
Secondly - text books solutions, even from the best b-schools are rarely well written, since they are written by caseclubs of these schools, not by the professors or experienced consultants. I would say that at the top b-schools people are not well-prepared in general since the interviews are pretty relaxed with the students getting 2-3 offers easily.
Thirdly, in real life you should start with clarifying questions:
- What's the measurable objective of the client - NPV, ROI, etc
- Clarifying the business model
- Any question that can help you narrow down your structure
Let me give you an example:
1) If the objective of the client is to calculate synergies, then you should have a structure around synergies (revenue synergies, Cost synergies, financial synergies, costs and benefits)
2) If the objective is different, then you can ask the clarifying question about the synergies. "Do we expect any potential synergies?".
- If the answer is yes - that should be the part of your structure. Where exactly - depends on the objective. If the objective is valuation (NPV) - then it should be a separate bucket since the NPV for synergies is calculated separately.
- If we expect no synergies - you don't even put it in your structure