Personal Finance Question, with Real Estate Involved

[Landon S.]

I was wondering if anyone had heard the rule of not spending over half of ones' savings on anything if you have no debt. I am graduating from college in May 2013 and already own one house jointly with my parents. I have been renting to three roommates for three years; their rent paying all payments and expenses. I want to see what BP members think about if I am in the financial situation to be able to invest half of my savings into another rental property at this time.
I can give more information if needed.
Thanks for reading and I appreciate honest opinions.