For this example we'll rebuild the GDAL Precise package.

 1. Let's download the files we need from [https://launchpad.net/~ubuntugis/+archive/ubuntugis-unstable/+packages?field.name_filter=gdal&field.status_filter=published&field.series_filter=precise Launchpad].
    We need to download the {{{.orig.tar.gz}}}, {{{.debian.tar.gz}}} and {{{.dsc}}}.

    {{{
    $ cd ~/vm/ubuntugis/packages
    $ mkdir gdal
    $ cd gdal
    $ wget https://launchpad.net/~ubuntugis/+archive/ubuntugis-unstable/+files/gdal_1.10.0.orig.tar.gz
    $ wget https://launchpad.net/~ubuntugis/+archive/ubuntugis-unstable/+files/gdal_1.10.0-1~precise1.debian.tar.gz
    $ wget https://launchpad.net/~ubuntugis/+archive/ubuntugis-unstable/+files/gdal_1.10.0-1~precise1.dsc
    }}}

 2. With these files downloaded, we simply need to extract the {{{.dsc}}}

    {{{
    $ dpkg-source -x gdal_1.10.0-1~precise1.dsc gdal
    }}}

 3. Then you can {{{cd}}} into the folder and update the changelog for a rebuild or make change to the package if you want.
    
    {{{
    dch -p -D precise -l precise "Launchpad rebuild for Precise"
    }}}
 You can then open {{{debian/changelog}}} and add entries if you have made other changes to the package.