I have rolled my own RPMs for OpenSUSE TW. I learned about the build process from a site aimed at Fedora and got the syntax right(ish) by looking at a bunch of official .SPECs from the OpenSUSE project. I also looked at packaging .debs, but that looks like an utter pain.
This matches my impression and experience, and I've been surprised to see many commenters here write that they found DEB packages to be simpler to write.
Perhaps as openSUSE users we both found the whole process easier because openSUSE drew us to OBS, and that made actually building the package easier?
RPM is much simpler than .deb, so guide is not necessary. It's just a simple .spec file with few headers and sections. See src.fedoraproject.org[0] for Fedora .spec files (click or search a package, then click on Files tab, then .spec file).
However, Fedora uses "convention over configuration" principle, so a packager must know Fedora conventions to package a program properly.
I find the Debian maintainer guide helpful enough! To me the difficulty difference is not large, but I like the simplicity of managing just a single spec file for RPM source packages.
