Here is a link to a basic model - http://monetizepros.com/tools/template-library/subscription-revenue-model-spreadsheet/
Depending on the purpose of the model you could get much much more elaborate or simpler. This base model will help you to understand size of the prize. But if you want to develop an end to end profitability model (Revenue, Gross Margin, Selling & General Administrative Costs, Taxes) I would suggest working with financial analyst. You biggest drivers (inputs) on a SaaS model will be CAC (Customer Acquisition Cost, Average Selling Price / Monthly Plan Cost, Customer Churn(How many people cancel their plans month to month), & Cost to serve If you can nail down them with solid backup data on your assumption that will make thing a lot simpler.
Let me know if you need any help. I spent 7 years at a Fortune 100 company as a Sr. Financial Analyst.
I have ample experience valuing SaaS-based business models from my recent operational experience within a SaaS business and my previous experience in investment banking. Happy to provide more information, but a "good" projection model will require a strong (and well thought-out) operational build-up. The more details, the better.
You should check out knowlium.com. They have a wicked projection tool that ties in all financials into your business plan.
Yes, I share all my SaaS excel models at www.TheSaaSCFO.com. All are free to download. I have a revenue model, expense model, and many SaaS metrics models.