It might sound obvious, but it is not. Consulting projects start with a structure to lay out all the questions that need to be solved (let's look at the market, let's check our competitive advantages, etc. etc.) Some branches of theses "issue trees" (I made hundreds of them at McKinsey, Google "McKinsey issue tree" and you get a lot of examples) might turn out to be dead end streets, some branches might have to be expanded, re-written later on in the project. As more analysis comes in, the solution of the project will emerge, documented alongside the structure of your initial workplan. At this point I would say: cut, take a break, throw away the structure. Now that you have something to say, worry about how to say it. With the benefit of hine sight, build the structure that tells your story from scratch. Problem structure does not equal presentation structure.