At this stage with the main light sources in place, I took the low quality rendering into Photoshop, and started tweaking a bit. I quickly confirmed that most of the colors were way too saturated, producing an image that was way too warm. Quick try with Adjustment Layers provided the direction I should try (Fig.14). I also noticed that the side walls could use some specularity to accentuate the damp feeling and that there was no nice main specular on the street...
I proceeded to fix those things. Light colors got desaturated and even turned slightly blue. The light coming from the sky was now almost gray.
The lack of specular on the street was fixed by duplicating the main light, turning off Affect Diffuse option, and using the Place Highlight tool to position it in the right spot (Fig.15). Fake? Sure, but looks good, and I couldn't achieve it with the main lamp placed where it's placed in the scene. If it was a real life movie set, it would probably be handled in a similar way by placing a light source just so.
The whole composition was starting to look unbalanced, gravitating towards the right side. I therefore added a light in the doorway down on the street level to the left in order to balance it a bit. There's also an angled box, invisible to the camera, shaping the hotspot to resemble an open door - yet another trick here (Fig.16).
The walls were turned into a Shellac Material, with a VrayMtl in the shellac slot (Fig.17). After some tweaking, I achieved a nice looking, damp wall, catching the highlight from that little square window.
The image was starting to look quite good now but a few tweaks were still required. The metal railings needed a reflective VrayMtl, the little metal roof high above the street needed to look wet, too. But the main problem was my 'preview' windows. I solved that by turning the lights to be single sided, and duplicating them. The duplicate is way weaker, as it serves only to illuminate the wall recession around the window. Now what's behind the window is another fake - it's simply a self-illumination map, using a photo of a window from the outside, at night (Fig.18).
It'll do for a still image, but it won't hold up for camera movement - we would need at least some simple interior then. Fortunately we are working with a still this time.