I want to make one for my sister's birthday.
I just recently made one for my boyfriends birthday. I used a 11X13 sheet pan for the main body (I did 2 layers and filled in between) and for the boobs i used the wilton sport ball cake pan, its two halves of a ball and worked perfectly. I cut into the sides of the sheets to make the waist and then covered it all in fondant. Good luck!
Google "corset cake" and "bustier cake" and you'll find a lot of good tutorials. When I did a bridal shower bustier cake I used a 12" heart pan and the Wilton small sports ball pan for the "girls." Covered the "girls" in flesh colored fondant and the bustier in black then decorated w/ pink accents. (the pic is in my gallery). There are so many outstanding bustier cakes on this site you can get a lot of inspiration. You could also carve a 9x13 cake if you want more of the slim torso look. It's a fun cake to do... enjoy!
Check out the one in my photos. I just used a 1/4 sheet pan and carved it.