One way that you could do this is to start with a full width header layout then edit the css. In here choose the box tab and select the outer wrapper, it should be just below the full width header.
With this selected you can move down on the page by adjusting the top margin value. In my test I just set the top margin to be 250 px. This put the content area down 250px on the page well below the header.
What have you tried and what are the results you are getting?