Though it doesn't seem like it, writing a business plan for your type of business is, for the most part, similar to writing a business plan for any other business. The differences will mainly be that you may need to build in some additional detail in the Marketing Strategy section of the plan to detail out all the different Social Media channels that you'll be using and how you'll be using them.
So, that said, I think you'll find lots of relevant information and help in the "How to write a business plan" section of our How to Articles. You can find that section here:
And like all business plans, use what is useful to your plan and leave out the sections or information that doesn't apply.
[Editorial note: We do try to avoid making sales pitches, but this question is exactly why Business Plan Pro was developed and is the market leader. We now also offer LivePlan, an online business planning solution to help you plan and succeed.]
See if you have a local Small Business Development Center (SBDC), Business Resource Center or SCORE office to get advice on where to begin. You can check the list on Bplans.com (http://www.bplans.com/business_planning_resources/sbdc/ or http://www.bplans.com/business_planning_resources/score/). Your local Chamber of Commerce office should be able to provide some resources as well.
On Bplans.com there are over 500 sample business plans that you can learn from. Here are links to a few agriculture type business plans that you can refer to for examples:
And, we have one sample of a plan from a Hydroponics Farm as well:
Bear in mind, these are for examples only. The financials for these plans will be specific to the areas that the authors wrote their plans for and will will be quite different than yours. You'll need to do some research as to the financial costs in your area to make your plan as accurate as possible.