What I did when i made Fran's hat for my friend was i made a base mold out of paper mache. let this dry for a day or two. While this dries, you want to fuse a layer (or two!!) or extra thick fusable interfacing to a large piece of pleather (or another similar material). When the paper mache form is done, mold ithe pleather around the paper mache form until their are no wrinkles. This will require you to make all kinds of pleating!! When you are done, you want to sew a circle that is aprox. the circumfrence of your head (plus abut 4 inches). cut a smale line through the center of it that is just big enough for you to fit your hand through and sew this to the bottom of the large, spherical type object you made earlier.
Now you stuff: you know those styrafoam beads that are inside of beanbags? You would be surprised how good they are for making hats. They can fit into the small creases and are also very light weight. We ripped ours out of an old beanbag, but you can also buy them. Stuff this through the hole you made in the smaller circle and when you are done, close it up. You make the eyes the same way, just with a little bit of variation in the coloration of the fabric. (I mean, they are eyes!)
I really hope that i helped...