Begin by identifying the major shapes:
Cars, pavement, sky, overpass, nearer building, distant building, mountain. 7or eight shapes. That should be simple enough. If you come up with more than 12 shapes, see if you can find a way to combine ones that are near one another and similar in value. An example might be the mountain and the distant building.
Make a simple pencil sketch just outlining the major shapes. This is to help locate the shapes relative to each other. We don't need to know what they are, just where they are.
Now, for each shape, assign one of the 5 values (1white, 2 light grey, 3 middle grey, 4 dark grey, 5 black). Write the corresponding numbers in the appropriate shapes.
On your sketch, paint the whole page light grey, except for any whites, which must be reserved.
Do this on 3 more pieces of paper. You'll have 4 identical studies, each one showing the whole page as a light grey wash that, in this case, covers everything except the two white cars. Put one of the studies aside.
Now, when the remaining 3 studies are dry, paint everything middle grey, except the light greys and the whites. Put one of those aside.
When the 2 remaining studies are dry, paint them all dark grey except for the middle grey, the light grey and the whites. Put one of those aside. See where we're going with this?
Now on the last remaining study add the blacks. When you're done, you should have 1 study that shows how the scene looks with only layer number one applied. You'll also have one that shows how the scene looks with two layers, one with three layers and one with 4 layers . When these all go up on the wall we'll have 15 different people's examples of seeing in step-by-step layers. That should make an impact.