Step 1: Dummy
I first built a duct tape seiwng dummy by having my wife and daughter wrap duct tape around my torso. then we cut it up the back and stuffed it. I mounted it and had a good dummy on which to build the costume. The picture below shows a long sleeve shirt (costume inner liner) surrounded by a plastic frame I built out my my kid's K'Nex pieces. Worked better than expected. On this I mounted 1/4" carpet padding foam and then I stuffed poly fil under that. Wrapped the whole thing in nylon and sewed away.
Step 2: Arms & Legs
FOr the legs I used a pair of sweatpants for the inner liner, added a nylon outer layer and stuffed in between. Feet were slippers wrapped and stuffed.
Step 3: Head & Final
I glued together styrofoam squares, carved out the inside for my head adn then carved it like Stay Puft. I glued carpet padding on it and then covered in nylon. The hat, ribbon and bib were simple sewing projects.
That's it. I hope you liked the costume. Here it is in final form with my wife as a Ghostbuster!. Check out the video on youtube.