After I draw up the design, I'll take the image to a print shop and get copies made according to the size of the piece and the amount of colors used. So if something is going to be 3 x 4 feet and has five colors, well needless to say I'm going to have five stencils (one for each color) at 3 x 4 feet!!! Then I have the wonderful task of sitting down and cutting them out.
To save on money and blades, I get everything printed in black and white on regular everyday paper. It's quite fragile, especially for the larger designs. But I've figured out a way to store them for repeated use.