This will look good when completed
. A nice bit of 60's urban grime.
By the time you have glazed and weathered (yes, weathered) the roof this will become translucent and therefore diffuse the light. Which, in turn, will soften or eliminate the shadows cast in the open arches on the backscene (assuming a single light source).
As Tony alluded to earlier, I think the train and arches in the background would appear much darker as would be the case when looking into the train shed from the outside (unless of course the roof has been removed!) going by two photographs in my collection. Manchester Victoria in the early 80's (mine) and Harrogate in the mid 60's (one of my dad's).