Step 1: Tools
You will need:
leather punch (recommended)
Step 2: Select a Purse.
Lots of metal on the purse helps, and leather is better than vinyl (since it is going on your head the leather breathes better and is less scratchy) . The purse should be at least 12"x10" to fit your head when cut out.
Be sure to parade around the store with several purses trying them on your head ( in front of the mirror with the most people..have fun) .
If you can find one with a nice arch where your neck goes, great.
The measurements on the greyscale picture are accurate, if you enlarge it and print. (Leave 1/4 inch for sewing)
Step 3: Symmetrical Cutting and One Seam to Sew.
Trace the right shape with some leeway for sewing, cut out the leather and then pin or tape it together backwards to sew with the stitching on the outside. Most of the sewing will be around the crown of the skull. With optional reinforcement sewing elsewhere.
The red dots are where I did most of the sewing. My machine wont do leather so i punch starter holes all along the area to sew with a needle. (close together about the length of long stitches )
Step 4: Plain Form Trial
Make sure the part on the base of the neck is not too long or it will annoy you after a long wearing session.
Step 5: Straps and Flaps
With extra scraps cut to form some good shapes about ear size or larger and make ear flaps and a strap on top with any buckles you have available.
Before you sew on the ear flaps, make sure that you have clearance for the strap from any goggles you may make later. Check clearance of both the worn or up on forehead positions.
Step 6: Adding Hardware
Rivets, nuts and bolts, snaps, and those things that go in paper holes and splay open, are fast and easy to spruce the helmet up.
The leather punch really helps here since the holes tend not to tear when made with the right tool.
I used a paper splayer thing to hold the forehead strap in place since i didn't have a proper buckle.
I also used one to shorten the purse's shoulder strap so I could move its connector with no sewing, on the cut off and shortened version of the shoulder strap (now chinstrap).
Step 7: Go Make Other Accessories....