I got a question. How do I create custom rigs in rigify made from an armature that I didn't rig to a mesh yet but I created the armature? I believe I would be able to do this because I read somewhere that you can add samples or even generate a rigify rig from a rig you built yourself from bones. But I have been unable to find a good tutorial on how to do this. Any help would be appreciated thanks. The reason I am asking this is because I get the impression that rigify allows you to make non humanoid rigs and rigs with unusual anatomy.
You can absolutely customize your Rigify Meta Rig which would allow you to rig (almost) any character. The "secret" is in understand the Building Blocks or "rig types" that Rigify provides.
I made a tutorial series on exactly that. Here is the series page
Or the youtube playlist
I hope this is a reasonable "self-promotion". There is very little info on this topic. I learned the basics from this video by Ivan Cappiello (one of past maintainers of Rigify)
And of course, there is the Rigify manual which can be very useful. However it is has been lagging behind the actual development of the addon. The 2.8 manual actually does not include images as of this writing.
So it may be better to look at the old version of the manual https://archive.blender.org/wiki/index.php/Extensions:2.6/Py/Scripts/Rigging/Rigify/#Advanced_Usage