Photoshop rendering basic techniques

Very simple exercise where two plans in the form of line were given and following some indications from Jamie (our teacher) we had to render it using different Photoshop techniques  (collage, bucket fill, brushes, etc)

The result:

Quite happy with the result, but there are still a couple of things that need improvement.  The drawings need more definition in terms of hierarchy, as the trees seem to be at the same level of the paving. I have tried to reduce the opacity of the trees in order to see the line work, but apparently instead of reducing the opacity I should instead define the tree layer blending mode as multiply, keeping the full strength of the color.