Most of the responses here are about what I believe Andy would see as the Version 1. But he talks about the step BEFORE diving in too deep into this. His approach is an exercise about getting to know the business. And using a single report as a guide/goal to help focusing the people you talk to. This one report will probably be thrown away when version 1 comes along which includes the whole subject area and allows for obtaining the same report again (but implemented in a more solid way).

The big thing for version 0 is to get to know the environment in which the data warehouse is going to operate (where are the original data-sources, how reliable is the data-input, who is fudging data on the way to the top, who will be obstructing any change, who will sponsor the project, etc, etc). Delivering the actual version 0 report is just a bonus to show your merits to management, but the real deliverable will be YOUR knowledge about the business inner workings, which will increase your chances of success for version 1 many-fold.