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 business plan contains several main elements. First, it lays out the mission and the goal of the business. The plan will spell out whether your company is in business to serve a greater good or simply to fulfill an unmet need. Determine whether your business will serve other businesses or supply products to consumers. These are all important elements that should be included.