You should probably have some modeling experience before you try to make conforming clothes. They aren't easy to make, and if you don't know anything about building your own 3d models, you'll probably find it very frustrating.

Here are a couple of clothing tutorials that use free modelling programs:

http://www.morphography.uk.vu/modtut1.html

http://poserpython.com/ClothTut1-1.html

The first uses Anim8or, the second uses Wings3D. Both can be downloaded for free.