It might seem a little counterproductive to build a business plan before you have a business purchased to plan for, but using the free 3-page business plan template at https://www.lawdepot.com/contracts/business-plan// will surely help you in several ways.
As you proceed to find the best business to purchase, the bank or some other lending entity will need a much more thorough plan.
For now, depending on the type of financial arrangements you anticipate securing, this 1-2 hour exercise will help develop your mindset more carefully.
Remember, this is a big decision, so our job in this book is to acquaint you with anything and everything that might increase your odds of success.
You will find the FREE 3 PAGE BUSINESS PLAN TEMPLATE HERE: https://www.lawdepot.com/contracts/business-plan