I haven't designed a stand alone mecha for a very long time. this rough version i did is for light/shadow purposes. the final version will be much more detailed, colored, and with a background. i used books from masamune shirow(appleseed) and
kawamori shoji(macross) for reference. kawamori just released a book this year of his artwork, including sketches for patlabor, armored core, eureka seven, and gundam. i'm not sure if it's available in the states, but it's very good for getting ideas.