I completed the migration to koji of my own personal build system to handle a set of local RPM packages for Fedora. I'm quite satisfied, as the installation instructions are rather straightforward and well documented. The possibility to use external repositories for released fedora packages is needed in my case, as my local packages come as an addition to fedora packages, just like epel needs rhl/centos, or rpmfusion needs fedora.

The necessity to merge the external repo (which is huge!) with the local one (which is small!) causes the mergerepos process to take some time to complete, and some memory resources (2Gigs for the genpkgmetadata process), so it is better to reserve enough memory+swap on the koji builders to handle this task. The kojira service, which is dedicated to this periodic activity can be disabled, and the repositories regeneration manually started when needed.

The fedora releng team provides on FedoraHosted some scripts using mash and the kojihub api, to populate a tree with the latest packages for each release of the distribution being handled in koji, to sign packages and to push them to an central location. These scripts can be reused easily in a custom setup.