Don't worry, Mom, I'll still make one for you.
Ok - this is the easiest thing to make, and I swear, the versions in Hilltribe were exactly like this. And their versions were $50. (I scored a great deal on the fabric in Toronto's Fashion District - it was $1 a yard, with a minimum 5 yard buy. I think I used up a maximum of 2 yards for this, so my cape cost me $2. Feel free to hate me.)
Here's a little diagram that might help.
Here's what you need to do.
1. Decide how long you want the cape to be. I decided I wanted mine to be mid-thigh. Measure from shoulder to mid-thigh - and write that number down. Let's call that number A.
2. Decide how wide you want the cape to be. I wanted it to hit halfway between my elbow and my wrist, so I held my arms out straight, and measured from mid-arm to mid-arm. (Imagine a scarecrow.) Let's call that number B.
3. Now cut a rectangle, whose length is 2 * A, and whose width is B. (See picture below.)
4. Grab some tailor's chalk, and draw a line which divides the rectangle into halves on the breadth, where you'd expect to see the shoulder seam (in the diagram, I've marked it shoulder seam, except there's no seam, since there's no piecing here at all.) (For the math/geometry people, you've now drawn two rectangles that are A * B in dimension.)
5. Now draw a line which divides the rectangle into halves on the length - mark this line from one end of the rectangle till the shoulder seam. (One of the rectangles will be divided into two rectangles that are A * 0.5B in dimension.)
6. Cut down this second line (drawn in step 5). This forms the center front.
7. Draw out the back neckline, and cut it out. (The solid marked-area in the diagram below.
8. All done! Wear your cape smugly!
Another clear-as-mud tutorial...