sorry got bored, seem to get bored watching that type of video. Prefer to see cities and play them more than watch people make them.
Greyscale is pretty simple, best to use the program I've put up here just to get the base picture, saving alot of time working out how many pixels in each direction you need. And then just choose a base colour an painting it all over the canvas before saving it. Before saving it, you can outline some basic areas so you can be sure to get some flat ground. After saving it, open it in a picture program that can work greyscale, (Most do) and just use variant colours of white, black and dark and light metallic colours and paint away. (All colours best to paint with a spray gun and at a very low opacity, around 5-10%, gets a good resulting effects after being imported.