Here's what I did:
took a series of measurements of myself from the floor to my knee, from my knee to my hip, from my hip to my neck. Also from the shoulder to the elbow, then to the wrist.
Each of these measurements corresponded to a same length of 1/2" metal pipe. At each joint (except the ankles) is a 4-way, 90, 30, or 45 degree screw on connector (see pix). Using a pair of channel locks, you basically assemble a tubular skeleton that is secured to a wooden base--to which you may want to attach 4 casters for ease of movement around the work area. I also needed to create a "3rd leg" that protruded from the bung hole to add stability. Remember to position the arms out in front using 45 degree connectors at the shoulders and elbows. This is done for ease of access to the ribs and under arms, as well as "pre-stressing" a latex skin.
At this point I bought some 2" upholstery foam and duct taped it onto the skeleton in layers to form the basic core. Then, dressed in form fitting thermal underwear, I had a friend wrap me in successive layers of duct tape. In the photos you will see that I did the bottom half of myself separate from the top---don't do that. Do a single wrapping, as this will eliminate incorrect positioning of the two halves on the skeleton. This is why my torso looks elongated on my mannequin. Afterwards, I had my buddy cut me out of the suit with a pair of blunt edge scissors, very safe.
I then dressed the foam cored skeleton with the duct tape shell and proceeded to fill it with "Great Stuff" can foam. The mistake many people make with using this, is that they try to fill the entire mannequin with it. Not only will the stuff take a million years to cure, but it'll cost you more-----which is why I wanted a foam core that consumed about 75% of the interior, leaving the spray foam to fill the remaining 25%. I felt that the liquid foam would reach and fill all the knooks and crannies better. The key to getting the foam to cure quickly, is to strategically cut incisions into the duct tape shell and spray in a mist of water from an old household cleaner bottle, then inject the foam into those areas. Foams need moisture to cure, and this will get the job done nicely. Some foam leaked out of the incisions, I just cut it off later on. As the foam is curing, I took a tailor's measuring tape (flexible) and taped the circumference of my neck, shoulder/ arm pits, chest , waist, buttocks, and so on. If you're mannequin doesn't measure up, just shoot in more foam, or add tape if necessary. Those measurements shouldn't vary that much.
Lastly, I bought some Plasti-Dip in a spray can and coated the entire dummy. This will help keep the tape from peeling up, and give the dummy a uniform, flexible covering. Hope that helps.