If the light is only coming through that window, it's un-natural to see the wall in which the window is lighter than the other (triangular) wall. That promotes the illusion that we're seeing a prisma from outside rather than an attic from inside.
Having the same horizontal lines going through both surface doesn't assist the perspective either. Try to use different sizes or at least offset them. I'm afraid you use too much contrast between the different "plates" in your second picture. Ideally, volume would have higher importance than texture details.
I like the lightning effect, though.
