Looks that way to me too Jeremy, which is strange, since the camera was level according to its internal indicator. So I snapped on the grid in Photoshop and found that the barn actually was a tiny bit on the slope. That's a pretty new barn, so I doubt the roof really is sloping. The only thing I can attribute it to is lens distortion, though that should have been taken care of by the profile correction I gave it in ACR. Ah well, here's a version slightly distorted back the other way to make the roof straight.
Damn, after I posted it I pulled it up from LuLa and it still looks a bit sloped. Well, we'll just accept the idea that the barn slopes.