I approach it as a series of ellipses.
A wide brim picture hat like the one shown here, even though it is soft transluscent layers, is still based on ellipes.
I always draw the head first, then fit the ellipse at the base of the crown to the head. The crown is then projected at a right angle to that ellipse. The brim is based on an ellipse that expands out from the crown ellipse.
If the hat is placed on the head on an agle then this whole arrangement of ellipses and right angles extends from that first ellipse at the base of the crown…which positions the hat on the head.
The drawing at the bottom is of my friend Tziporah in a fabulous vintage hat.
Look for more of these little lessons from my book – DRAWING THE FASHION BODY. I am investigating turning it into an E-BOOK but until I do it is available for $30 – B & W diagrams and templates, spiral bound. Contact me to order the book. More info is available on my website