Strange that you should post this up as I've just finished making a steel scoop for a good friend of mine to go on his P100 pick up truck. here's a couple of pics:-
Making the side panels with the top & bottom edges formed into a radius
After welding the sides on, the top was formed with a slight crease down the centre. I then folded a 15mm strip of metal to form a swage line to run down the centre of the bonnet.
A little bit of filler to finish it off
followed by some primer
then some satin black to protect it until the truck goes for painting
All in all a pretty straight forward job. The same procedure can be used to make this style of scoop for pretty much any bonnet
cheers...Nige