Writing the business case document is the end goal of this process. Researching it and defining it comes first, before you write anything.
So, as in all things, preparation is key. Getting things right at this point can allow your work to be focused on productive issues, eliminating time wasted on unimportant side issues.
Begin by looking at how the idea came up. It may not have been your idea, that may have come from someone else, and you have been asked to take the idea, evaluate it and develop and present a business case for it.
From the terminology used, i.e. “business case “, whoever has commissioned the work from you thinks it is the correct decision and is looking for you to build a case to support the project and enable a decision in its favour.
However it is your job to look at every aspect and check it is the correct move for the business.
So start with whoever came up with the idea. Talk to them, find out everything they have to tell you on the subject.
What do you need?
Then consider how big a task lies in front of you. Do you need any additional resources- time, money, equipment, personnel? Who do you need to approach about that? Will they give you what you need? Before you ask for anything, check out what is already available within the company.
Is there any data held or gathered by other departments. Can you get the research you need from a market report? Do the company already subscribe? Would it be cheaper to buy a report than duplicate the research?
Your marketing department, and market research function may be a good source of information here, or New Business Development if you have such a department.
Once you have got this far and have an outline idea of the way things look, it may be worth asking for a preliminary meeting with a couple of the decision makers, and make sure you have covered the angles they will want to analyse.
It is at this point that you will be able to decide if you don’t think this is a viable project. If so you should propose that you pull out of producing a business case document.
Your management may still want to see the documentation, but in that case it would be a report rather than a business case proposal, which by definition advocates the initiative.