Mr. Sibley,
I feel awful silly and presumptious to even think of critiquing your work or even offering suggestions, but that doesn't seem to stop me from putting my foot in my mouth.I think (dangerous words) you are probably right about it defining itself as you continue. I watched my work do that to my own amazment, but you already know that.
In looking at the drawing and the reference, it seems that the areas in the shadows of the barn, may not be shaded enough. Perhaps the contrast of the upload just makes it look that way. If I'm in the sunlight and look into an unlit barn, the images in the rear of the barn would be less defined.
Don't think me foolish, I'm in awe over your talent.
Steve