Building a rental portfolio

[Joe Salimao]

Hi guys,
Here is my question.
How does one build a rental portfolio of say 30+ properties without tieing up your own money in the process? This is my goal but I see that it may be extremely difficult to get in and out of a property at <70% LTV. The reason I use 70% because this is the current max of a refi set by Franny/Freddie.
If I don't do this I don't see how I could get out without leaving my money in the property. If I left mnoney in say 10 properties I would be out of cash completely.
Maybe I can find mortgage companies that refi at a higher rate but this will of course affect cash flow. I can also look for subject-to deals.
I hear a lot of people say landlords only need a property at 80% LTV minus repairs but I am assuming they are leaving money in the deal.
What do you experienced investors who have a large number of properties do? Do you just have a large amount of cash to tie up?
Thanks for being patients.