My solution as a consultant was to build some artifact that we could use as a starting point. Otherwise, you're sitting around spinning your wheels and billing big $ and the pressure is mounting. Building something at least allows you to demonstrate you are working on their behalf with the promise that it will be refined or completely changed as needed. It's very hard when you don't get people who can send down requirements, but that was like 100% of the places I worked. I very seldom ran into people who could articulate what they needed until I stepped up, showed them something they could sort of stand on, and then go from there.

Mythical Man Month had it all--build one to throw away.