I create my helmet shape from a picture of a great quality reproduction.
I usually design only one half of the shape and than I reflect it in order to preserve a perfect simmetry; in this case I wanted it.
I created shapes overlapping themselves and then I extrude them: I like to have perfectly clear graphic at the end of my work, so I usually extrude different elements.
I hate to open a working file after time only to find a busy overlap of shapes of different colors on a color background.