Daddy Long Leg
+1y
The easiest way would seem to be to cut a panel from your existing hood down the center and roll it until you get the shape you want, then weld the front to where you cut and weld fillers to the sides. You might want to add more material to the cowl end but the roll would be so small that depending on how tall the hood is, the difference might not be noticable, also be careful to make sure the hood doesn't hit your glass. I plan on doing a subtle cowl on my 330i and that's exactly how I intend on doing it.