From a freshly created buildout, create a src directory if its not already there and cd into it. From there run:
> zopeskel plone3_theme
This creates a project for a theme for Plone 3. Answer the questions, and a new egg will be generated for you in the src directory. Don’t forget to add this egg to your list of buildout eggs!
If you cd into your new theme, you will see a contextual list of zopeskel commands. With respect to themeing, you may want to add portlets, localization, or views. To add any of these types of content to your theme, run the addcontent command. i.e.:
> zopeskel addcontent portlet
There is very complete documentation on creating theme templates with zopeskel at the following sites: