Do you mean custom as in original? I've never made any original costumes that aren't based on an existing character, but I've done some "generic" ones. For example, I have a Stargate SG-1 costume, but I don't cosplay as any of the female characters from the show. Just myself in a Stargate uniform.
My character is called Jane. She's a dark, deadly assassin who is skilled in combat and weaponry. She is very secretive and tends not to trust people. She picks out her victims, typically criminals who are too powerful to be touched. She is often found in tight spots. You can see images of her here: