Most people start investing real estate by buying their personal residence. Yet the majority of Americans will stop there in terms of building their real estate portfolio. This is because when people are motivated to buy their first investment property, they are often told they will need a 20- or 25-percent down payment. Finding it tough to save for that large of a sum, most go no further. However, if you are willing to move from house to house frequently, there is a way to build your portfolio with smaller down payments.