Have you ever tried to create both Debian and RPM packages using OBS? Well, a little bit different from the package generation locally, but not that much ;)
Before continuing, you should prepare yourself with basic Debian and RPM packaging knowledge.
First, make a tar-ball for your source code, without any packaging information inside. Name it obs-sample.tar.gz.
Then for Debian packaging, you need the following files.
obs-sample_1.0.dsc: indicating you want to create a Debian package; the Files section is not needed, but the Build-Depends section is necessary.
debian.rules: the rules file for Debianization.
debian.control: the control file for Debianization.
debian.tar.gz: all the other files inside the debian folder.
For RPM packaging, you only need the .spec file as expected.
Finally, here goes the simple sample I created. Happy hacking!