The project proposal or project charter is the document approved by Management for a project to get underway. It actually will not usually include a Gantt Chart but instead a rough estimate of the timeline including major project milestones and estimated dates. The real details come after the project charter is approved.

Other than the project milestone summary, other items that should be included in the proposal are a description of the project, the business need, project objectives, high level project requirements, project risks, any project constraints and a summary of the budget. These things should all be high level, the details will come with the project plan (D&D Plan). The proposal should also identify project sponsor and project manager. These items are necessary to include in the project charter because management needs that information to approve or reject the project.