Making the Alley Surface

 Building the alley surface; curb and ground

On the plane I selected the vertical edges in the middle nearest the building and moved them closer to the buildings to mark the curb. I then used the insert edge loop tool to insert two more lines to set the width of the curbs. I dragged another horizontal edge near the front of the buildings to set a cross alley and used the insert edge loop again to set the width of that curb. I selected the faces of the alley way and then extruded the faces down and then deleted the extra faces created by the extrusion. Next I selected the alley way pieces and extruded them.

I selected the curb pieces and extruded them upward slightly. I then selected the ground faces on either side and extracted them.