If you had $20,000 to invest you could put it into a mutual fund. These are running around a 5% profit a year. After 7 years you could have $28,142.

You could use your $20,000 to buy tax liens paying 18% in year 7 you would have $53,991.08

You could  borrow $180,000 and use the $20,000 as a down payment on a rental property with a value of $200,000. Lets assume the rental income covers your expenses. The property goes up in value say 5% a year. After the same 7 years your would have a property worth $281,000. You would owe the bank somewhere around $179,580 and you would have equity of around $101,420.

You could  use the second option except in year two you borrow against your equity to buy another property.  Do this every two years and in four years you would have four rentals worth over $2,000,000. Your equity would be around $273,000.

Once the bank knows what you are doing and that you are actually doing it you would only need 10% to buy the next properties.

Personally, I do not like using other peoples money (loans) so at this point I would work on getting these paid off. Four properties are giving you a really nice living.

To summarize:

$20,000 invested

Net Equity in 7 yrs	Avg. annual return
$28,142	5.8%
$53,991.08	18%
$101,420	58.2%
$273,198	180.9%