I've just had a look at the widest part of the roof line of the first photograph (in full size view), and it does appear that the left hand side is lower than the right hand side, but if you are happy with it, that's all that matters.
With the third shot, I wonder if you've got some barrel distortion, which is why you can't straighten both the bridge and the mausoleum. You could try to correct it with software. If you have Photoshop CS5 see
http://help.adobe.com/en_US/photosho...4cc8e9c98-8000
Regards
Nick