Yeah, I remember when this whole thing went crazy. I've already made a comment on not being very helpful with rating system... I could help with one semi established, but I'm no good at doing it from scratch, I think.

That's from ages ago. The app doesn't let me reply to replies. No idea why. The rest is from today...

I like Vega's system for certain. I always try to do that and fail... So something like

Title & Rating
Fandom
Canon/Noncanon
Timeframe
Pairing (if applicable)
Content Warning

I was also toying with the idea of rating stuff more like you would actual books rather than television or movies, since this is a writing site. Obviously you wouldn't have "picture books", but maybe

Teen/Young Adult - Suitable for middle school and up.

Adult - Suitable for high school and up

Mature - Contains adult content or themes.

Add more.. be frustrated more... Whatever. :)