Supernatural OC Help?

I've been thinking about at least making a Supernatural OC in case I decide to use the character in a roleplay or in a story, but I don't want to do something that's been completely overdone. I also don't want to read a whole bunch of fanfiction to figure it out because I don't want a bunch of fanfictions to influence my view and understanding of the characters such as Cas and Dean.
So my question to you readers is what has been completely overdone with OC's in the Supernatural fandom? And would any of you have any tips for writing a Supernatural fanfiction, especially if I decide to have my character fall for any of the members of Team Free Will.

Thank you so much for the help!