Hi John
From your gallery I guess your using the 17-85mm lens IS
If you look at the photozone link your notice the lens is not a good performer in the distortion department at the wide angle end.
http://www.photozone.de/canon-eos/17...report--review
To correct for this the you need to correct for the barrel distortion before applying any perspective correction because the camera was not level.
You can get software to do these complex corrections but will it be worth it in your case.
The distortion is much reduced at the 24mm setting compared to 17mm so I would suggest using 24mm instead of the 17mm end for building work.
If you really need wide angle for building work then I would suggest getting a lens that has much less distortion at 17mm.