Jim's mask is a mask that needs to be bought. It can be bought online here ($27.99) / here search for a "jester mask". Unfortunately, after you have bought it, it wont look too much like the final product and you will have to make many modifications (see below).
For the face part of the mask, the top and bottom will need to be cut, so that just the white part is showing. The neck should be cut mid way as can be seen from the picture. Now cut off the mouth so that a zipper can be added, then rivet around the mouth which isn't as simple as it looks.
The upper portion consists of the leather strap that goes over the head to meet the ring. Attach the ring at the middle of the forehead. If you want, you can just use basic straps to hold the mask. The strap underneath the ear is attached to the ring in the back of your head. No rivets. The strap on top of your ear is connected to the same ring at the back of your head. No rivets on this one too. This one pertains to the strap that wraps around your head. I recommend measuring your head's circumference and the strap should be a bit longer. This strap supports the whole mask and is the most important of all, therefore it is riveted. It is also connected to the ring at the back of your head. You can also add another strap that is fastened below your chin for a better hold. Be sure that it fits just right.