The pencil is an excellent start to a line drawing that can be finished in Photoshop using a graphics pen.

The mechanical shading in the buildings and sky will be done with a line conversion technique. This is done by putting is shaded areas in the original Grayscale image (say, one of the buildings) on a separate layer, copying it to a New file, converting the New file to Bitmap mode using the Halftone Screen method (with lines as the pattern), Convert it back to Grayscale, deleting the white pixels (leaving the lines on a transparent background), and dragging it back into the original setup.