Why is the WBS so important to proposing a deal? You cannot propose a deal without a price. You cannot price without an estimate. You cannot estimate without a plan. You cannot plan without a work breakdown structure (WBS).

The WBS should also include the phases, activities, tasks, dependencies, milestones, and effort. Be sure that you also identify and capture tasks for analysis, review cycles, testing cycles, and meetings. These are often items that take up a great deal of time but are often not included in the WBS

However, the following guidelines apply to most estimation methodologies:
  Build your WBS by basing it on outcomes and not actions
  Base your WBS on all of the work to be completed, not just on the work to be completed as part of a fee-for-service effort
  Do not mix estimation methodologies within a project;
  Ensure that each item you create in your WBS does not overlap with another and is a discrete entity. 
  A good rule of thumb is that to stay at a manageable level of detail, go no more than 3 levels deep in your WBS. 
  Create your estimates based on the actual length of working time (not calendar time) required for one qualified resource to complete the task
  Other than the assumptions documented, create your estimates without thinking about who will be performing the task. 
  Create quick profiles of the roles that will be performing the work.
  Do not add buffer or contingency time to a task estimate in your WBS, this should be added uniformly at a later stage.
  If the requirements have imposed a firm deadline, you should work all estimates backwards to the appropriate start time, as a reality check. If the appropriate start time for that deadline is not feasible or is in the past, the project is probably not going to be successful with the current Scope of Work.