My daughter, at the last minute, needed a pair of round wire-framed glasses for the character she wanted to be for Halloween (Jade from Homestuck). She begged me to take her glasses shopping, but I decided to try making her a pair instead:
I used 18g wire. It was pretty easy. I just made wire circles like I do for my trees, but instead of making a bail I left the wire long to reach the ears. She then held the circles where she wanted them to be on her face, I measured the space for the nose bridge (in this case 19mm), and made the bridge from a piece of wire. Like I said, easy. :)