I have created a wiki page for this here:
https://wiki.contribs.org/Plex_Media_ServerWhen I first installed Plex there was a bug in the spec file causing a failure on install but after a lot of nagging they finally fixed it.
There is a handy installer script that automates updated etc now.
I believe the installer will do an initial install but I haven't tested that as yet - I just started using it to update my installation.
Please test and report back, or modify the wiki with your experiences.
It would probably be possible to create a contrib now, though I don't think it is worth the effort.