Vampire Cape: a Costume-Sewing Tutorial without Pictures

Drafting: 

Measure from the nape of the wearer's neck to the hem length you want, add your seam allowance to that (twice - top and bottom) and trace out either a rectangle or half a bell shape that tall on the fold. Cut 1 each from lining and cape outer fabric. Draft a collar shape. Cut one from stiff Pellon interfacing, and one each from your lining and cape fabrics. Make the interfacing a titch smaller than the fabric - 1 or 2 mm on the top and sides. If you use satin, be sure to use an appropriate needle or you will poke holes in the fabric or cause runs at each stitch entry point.

Assembly:

1. Make a stack: 1 collar piece right side up, one collar piece wrong side up, one interfacing - centred and aligned at the bottom. It doesn't matter what order the fabrics are in as long as the interfacing is on top and the lining/cape fabrics are laying pretty sides together. Then sew ALL THREE together on the top and both short sides. Turn it right side out, poke the corners out, press (you will need an iron), and topstitch only on the closed sides.
2. Zig-zag the raw edge with a relatively long/wide stitch setting, just to keep the edges lined up and together.
3. Sew the body of the cape by stitching the lining and outer fabric right sides together, along the sides and bottom, and turn it right side out. Do not topstitch it yet. If using a bell-shaped piece, leave twice the width of the collar unsewn at the top.
4. Find the centre of the raw edge on both the collar and cape, and mark it. Keep your mark within the seam allowance. A pin will work for this.

So then you have two pieces, each with an open side. Now we're in the home stretch:

5. Lay the cape on the table, lining side down. Lay the collar above it, as it will ultimately be. Line up your centre marks.
6. Then flip the collar down so it's on top of the cape, outsides together, and with raw edges lined up. Pin (if the cape is satin use clips - snap-shut barrettes, clothes pins, paper/bull clips will work if you don't have "wonder clips") the collar to just the cape outer fabric. Start pinning in the middle and work out to the edges. Sewing from the cape side, zig-zag the collar to just the cape outer fabric along the edges like a serger would, right over the collar’s zig-zagged edge. Remove pins as you come to them – if you hit one it will put a run in your satin which will never come out, and probably break your needle.
7. Lay your cape out again, with the collar flipped down as before. Lay the tie cords (or elastic with velcro) immediately to the left and right of the collar, with their raw edges lined up with the cape's raw edge, and pin/clip them in place. Sew them to just the cape outer fabric with a short straight stitch, within the seam allowance. Go back and forth three times per cord.
8. Then you press the seam allowance on the cape and lining in at the opening so it makes an M if you cut a cross-section. Because the collar is attached to the outer fabric, it now flips up, into its final position, wedged in the crotch of that M shape. Pull the ties up and away from the cape, like Grover's excited arms.
9. Pin/clip like crazy along the open side, making sure that the pressed edge of the lining and cape fabrics are lined up. You might be able to pull the cape shoulders on either side of the collar to get the lining and outer fabric to snap into a straight line. That helps ensure that both sides are aligned on the inside and outside of the collar, since you can’t see through the collar to make sure you’re sewing all layers at once. Slowly topstitch the opening closed, continuing all the way around the cape body. This will finish the cape, secure the ties, and lock the tray table collar in an upright and secure position.

You're ready for Hallowe'en!