Free model for calculating investment scenarios

[Lorenzo Bernasconi]

Hi there, 

I'm just starting off on my real-estate investing adventure and am wondering where I can find a comprehensive Excel model (for free) that will allow me to analyze the purchase of a multi-family home.  In particular, I'm looking to understand how much I would need to charge for rent in order to cover my financing expenses as well as understand how this might compare to other scenarios, e.g. purchasing a single home.

Thanks!

Lorenzo