Gwen Spicer has a great paper with a really nice versatile design that you can build, although she recommends the internal armature be made by metalsmith.
http://www.spicerart.com/publications/publications_assets/Spicer%20copy.pdf
She does have a similar design using PVC as well.
I believe that similar mannequins were built for an exhibit at the Wright Museum of Art at Beloit College while I was a student there. I’ll see if I can get a copy of the design for those if you would like.
