Thank you, this is (or could have been) exactly what I was looking for.
I installed off a LiveCD, and then downloaded updates and packages. /var/cache/yum totals 110 megabytes after I added the keepcache=1 parameter. I thought I had downloaded ~15 gigs of updates. I don't understand this step from your website:
"Next put all the rpms that you want in your repo, ..."
Either I have a ton of rpms that are sitting somewhere, or I just grossly misjudged the size of the files that I downloaded.
I think I need more time to actually know where files are, I just don't understand the filing system that Fedora uses. I'm using KDE, so I worked out that "gedit" was for GNOME, but the way that Fedora (and I'm assuming any non-Windows) systems organizes system files is just beyond me.