Thanks for all the *very* helpful comments. I didn't take the time to neatimage the sky (I thought it would fuzz up the building and lose some dof) but clearly I should have!
The clouds make a great backdrop for the building, which is nicely proportioned. The subject is slightly underexposed, giving it a pleasing low-key appearance consistent with the overall mood of the image. Great job.
Very dramatic sky indeed! Interesting perspective too. Seems very foreboding and ominous, like a scene from a sci-fi movie. A bit of noise in the sky probably due to over processing, but it's not too distracting.