Besides editing existing themes and developing from scratch, you can also obtain themes using theme builders. Theme builders are web-based or desktop-based applications where you can specify colors, layouts, and other styles for the different parts of a theme (namely, header, sidebar, body, and footer).You can then generate CSS files accordingly.
The most advanced instant theme builder is available at: http://redalt.com/tools/builder.php.
In the theme builder by RedAlt, there are four supported layouts. You can select any of the four layout styles. Take a look at the following screenshot overleaf:
In this step, you can select some options for the different sections, like ...