What Are Some Original D.i.y. Costume Ideas?

Halloween is rapidly approaching and I still can’t figure out what to be this year since my friend is going with my Carmen Sandiego idea.
I’m trying to avoid anything cliche or overdone, and also pre-made costumes [it's all sexy-this, and sexy-that, and I'd prefer higher quality].
I’d like to be a specific character [ie Zatanna from Batman] as opposed to something more general, like a flapper, and I’m not opposed to something sexy as long as it isn’t pre-made.
Anyone have any brilliant ideas?
Price isn’t really an object here. I’m just looking for inspiration, so pictures and links are also appreciated.
Thanks in advance for your answers!