If a document needs to be developed that requires input from other disciplines_Finance, HR, Property & Facilities, Marketing, Procurement/Supply Chain_ then most likely you are looking at a team building effort to get the job done. In any event, don't look at the task as only as a roadmap that leads to a profitable product or enterprise. Business plans are a great way to build team buy_in, force a thorough review of options, define objectives, establish benchmarks to judge performance, and help arrive at a plan_of_action. Ultimately, it can lead to a Project Management approach to implementing a plan and that can be as involved and detailed as is necessary.
A plan should include but is not limited to the following: 1. A statement of your business purpose 2. A description of your company 3. The goals of your company 4. The structure of the company (sole_proprietorship, partnership or corporation) 5. The product or service that you are selling 6. A market analysis of your product or service 7. Resources spent (time and money) 8. A financial plan to include financial statements 9. Information about the managing principals in the company 10. How you plan to manage and operate the company