Thanks John - that could be said of so many of us.
I don't think there's actually distortion. This was taken in the telephoto range of my G11, where I've never seen any. I think it's partly that there's a little convergence towards the top which I didn't bother to fix and partly that not much is true horizontal or vertical on this structure (I'm pretty sure it was a garage) at this point. I will look at the perspective and straighten it out - thanks for suggesting.