How do I create a nice-looking DMG for Mac OS X using command-line tools?

I need to create a nice installer for a Mac application. I want it to be a disk image (DMG), with a predefined size, layout and background image. I need to do this programmatically in a script, to be integrated in an existing build system (more of a pack system really, since it only create installers. The builds are done separately). I already have the DMG creation done using "hdiutil", what I hav