This is the build system used for my personal debian repository.
Use buildpkg tool (in the root directory) to build selected package.
See buildpkg --help for details.
By default, it will run debian/rules get-orig-source to prepare upstream source packages (you will need Internet connection to do so), then call debuild to build the package.
All the files in debuild/ directory are licensed according to <package-name>/debian/copyright file. Other scripts are put into public domain using CC0 1.0 Universal.