Why are the walls in my architectural renders look sloping and how to fix that?
Why are the walls in my architectural renders look sloping
Perspective
and how to fix that?
Camera shift settings
http://wiki.blender.org/index.php/Doc:2.6/Manual/Render/Camera/Perspective
He is exactly right.
Just one of the basic rules of shape and figure.
while shifting camera you should remember to keep it parallel to the ground (i.e. 90 degrees on x axis)