I wasn't planning to upload this, but my photobucket account wasn't working. For examples of costumes made using this, see my Catwoman and Resi5 Jill costumes.
I made this after having a couple of people asking how I made my catsuits, so hopefully this will be useful to someone.
Note: This is how I make them for me, with average female proportions. If you have larger shoulders or bust than hips, adjust the pattern accordingly.
The red lines are measurements. For all except the legnths, measure fully around the person.
For each section, draw it onto large paper (wrapping paper or brown parcel paper works well) as a rectangle:
Front = 1/4 of hips X body length
Back = 1/2 hips X body length
Arm / leg = roughly around the top X length
With these rectangles, use your other measurements to get the blue cutting lines -for the front measure where your waist and bust have to go, and join them up smoothly. For the shoulder and neck, don't cut them yet - sew it together with the shoulders square, then you'll see how much you have to take them in by, and then you can also cut a relevant curve for the neck. The back is similar, and is pretty much just two of the front pieces side-by side. It can be made as one piece or two, with the central dotted blue line either being a full seam, or you can just pull it in and sew it later to make the catsuit hug the arch of the back more. For the crotch I usually end up putting an extra little panel in, as show, before attaching the legs. This just gives it a bit more freedom of movement.
For the leg / arm, fold it in half to make sure it's symmetrical, then mark out the width for the wrist / ankle, and draw a line joining it to a point a few inches down from the other end. Then draw a curve going up to the top of the sheet.
general notes: Give yourself enough room for mistakes - cut a bit larger than you'll need and you can always make it smaller. Give a couple of inches for the zip to go in. The back measurements and front measurements are only roughly half for the bust, waist and hips - to be accurate,m easure them seperately. Stretchy fabric is advised.