You could try rendering the back row or two of buildings, then paste the image into the background or onto a one-sided square prop (or one of the cove props - RDNA has a free one) and then rendering the next layer of image in front of that and so on, or you could also render each layer sparately, with no background prop(s), save as TIFF or PSD and then open in a paint program and use the embedded alpha channel to select and then composite the successive layers.