This is a pattern for a super-basic Assassin's creed style hood.
Basically it's mimicing a regular hood but with an extra panel in the center that gives it the iconic peak and size.
The simplest way to make it is:
Measure the measurements you need. Take half of B (the size areound the neck) and draw this out as a line with two parrallel lines stretching from the ends upwards. Then find A, the curve height. Get your tape measure, string, whatever, and lay this on your pattern from one end of B, curving nicely to a point on the opposite parralel line. As long as A is the right length and it makes a nice curve, the height up the line isn't overly important. The final line, which is the front, can also be guessed. Cut two of this.
The middle panel is basically taking a rectangle that's a bit longer than A, narrowing it down at one end and adding the peak) at the other.
Simply stitch them together so that all the blue dots meet up, and so that the green dot on one side of the central section meets the green dot of one of the side sections. Then do the same for the other side. Hem the front, attach to your garment (or just to a strip of fabric about a foot wide if you want a hood that just covers your head and shoulders), and you're done.
The hood in the picture was made using a variation of this pattern. The side panels are the same shape as most hoods on store-bought hoodies, so if you unpick the middle seam you can insert the middle panel to give yourself an uber-easy assassin hood.
The lining of his hood has been cut slightly smaller than the hood so that it is constantly pulling the hood in around the face.
It is advisable to either use a stiff fabric or interfacing in the middle section - or at least the peak - so that the peak doesn't droop too much.