The game proposal is a much more formal document than the design document. It will be used to approach a publisher for possible funding for a project. If you are planning to develop the project with your own money, a game proposal is probably unnecessary.
A game proposal takes the design document to another level. It involves several issues that should not be included in a design document. After the design document has been thoroughly digested by the lead programmers or the senior members of the team, it should be included with the game proposal. Additional information should be included such as technical specifications, marketing, financial, and legal. I’m not going to break these down into great details, but the major sections are included. For a quick overview, you can refer to Figure 5.8.
Figure 5.8: Basic parts of a game proposal.