Thinking Holistically, Suppose a New, Unique Project Is Being Estimated

Thinking holistically, suppose a new, unique project is being estimated in which there is unstable scope. There is high uncertainty in the duration and cost of each work package. Uncertainty as to which work packages to include / exclude is abundant. A project of this type has never been done before and the customer is uncertain of what they want. There are no previous similar projects or a history data base of work package durations and costs to work from. Top-down estimates of total project cost and duration do not exist. You have a dedicated team of ten seasoned project professionals working for you. You worked hard to develop a well-structured WBS for the project. Each work package (there are ten) has been assigned (by you as project manager) to exactly one project professional to develop and complete. You wish to do a bottom-up definitive determination of overall project duration and cost. The customer wants cost and duration details. Under such circumstances, how would you proceed? What assumptions would you have to make? How would you come up with estimates as to duration and cost for each work package?