Decide how you will scale your model. If your model is five and a half feet (66 inches) tall and you want to scale the model at two inches for each foot of the woman's actual height, you would make the model 11 inches tall. You will be baking the clay in a conventional oven, so take into account the size of the inside of your oven when deciding how large to make the model.
Find a live female model to pose for you or take pictures at every angle of the subject's body. Either print them out on photo paper or use a Polaroid camera. If you are using pictures, tape them in front of you so that you can look at them as you work.
Form aluminum foil to give you a base or "skeleton" to work from and shape it into the model's pose. You are only making the thin framework, so it doesn't have to look like the model yet. Make sure that the framework is strong and anchor it to the cookie sheet with a mound of clay. You will be building up from this mound.
Add clay little by little and keep referring back to your subject or pictures to make sure the model is accurate. Work from the bottom up and don't try to add clay to the upper parts because the framework can warp and become distorted. Pay attention to minute details, such as the woman's subtle muscle tone. Make sure to keep the thickness of her limbs proportional. Use your fingers to add and form the clay and use a clay knife or utility knife to shave away any surface imperfections.
Preheat your oven at the temperature specified on the instructions for your oven bake clay. Place your model into the oven on a cookie sheet and bake for the amount of time specified. When the time is up, remove the model from the oven and don't touch it for at least 30 minutes. After it cools, you can remove it from the cookie sheet and paint it if you want, or just put it on display.