Halloween Witch

For this week's illustration friday theme 'haunt'.
I started with a small sketch in one-point perspective:

After painting the shapes in photoshop, mostly with the polygonal lasso tool, I merged all shapes of similar color to one layer. So all the windows are on one layer, the moon+street on the next, the shadows of the building on another, and so on.

Then I stretched and moved these layers a little to obtain a screenprint-like effect.

Finally I added a paper texture and some scratches and dirt with various brushes.
A similar technique is used in my illustration 'lost'.