For my Ion cosplay, I made a pattern that looked like this. http://i45.tinypic.com/2vnnfcm.jpg
When you're taking measurements for the collar, make sure that you don't take your measurements too small. What I did was I got stretch fabric(kinda important) so I could make the collar while being able to still fit my head in. It's important to remember that the circumference of your head is bigger than your neck, so don't make the collar small as possible. Otherwise, you wouldn't be able to wear it. And that would be unfortunate.
To make the collar stand up on its own I it in folded it in two layers, then attached it to the sewn shawl piece. Also, remember to leave enough extra fabric for hemming.
Here's the unpainted shawl that I made with the pattern. http://i45.tinypic.com/2m7i7m1.jpg
Good luck with your cosplay. ^^