Use the sample Makefile to help download source packages from a local Yellowdog Updater, Modified (YUM) server, sign packages, and upload new packages to the YUM server. See also the parent RedHat Package Manager (RPM) notes for information on setting up a build system and signing packages.
Source RPM must be rebuilt on all supported distributions. For this reason, the number of supported distributions (and revisions thereof) should be minimized to avoid otherwise needless package rebuilds. If possible, virtualize the build systems to save on hardware costs.
I usually scp the *.src.rpm from my primary build system to systems running other releases, run rpmbuild --rebuild ?, then copy the resulting packages back to the primary system for signing and upload to the YUM server. This is time consuming, and could be automated more.