How much detail are you looking for?
Script do just install it:
http://elinux.org/BeagleBoardUbuntu#Demo_Image
Build everything (except the root file system)
http://elinux.org/BeagleBoardUbuntu#Method_3:Manual_Install.28no_automatic_scripts.29
Or "create" ubuntu root file system from scratch, from ubuntu archive *.deb's:
https://github.com/RobertCNelson/omap-image-builder/blob/master/build_image.sh
Or rebuild every *.deb"..
http:// yeah your on your own for that...
Regards,