Making a Leather Mask?

I'm making a leather mask for a Halloween masked ball and I'm going to soak it and let it air dry, so it hardens and retains its shape. I already have paper pieces cut out for the parts, but I want to know how much the leather will shrink before I stitch all the leather together. Should I make the pieces slightly bigger or significantly bigger? Or should I make a mold to put it over while it dries?

By Adam M. from McHenry, IL