Try to Avoid Parallax
Who wants a building to look like it’s falling over?
If everything in the scene is approximately the same distance from the camera, or very far away, the parallax effect will be elminated or at least minimized.
The way you keep your verticals vertical is to try to keep the plane of your camera parallel to the vertical line of the building, which is not always possible, of course.
Wide angle lenses can help reduce parallax effects because a wide angle lens accentuates perspective, making everything seem further away. However wide angle lenses also have a larger field of view so there is a greater chance that things in the foreground (including the ground itself) are captured and then cause problems.
If you use a render engine like V-Ray, you'll have a guess parallax toggle, but if you don't, there are post-processing tricks to do the necessary tweaks!
If you have any question please, contact me, and I'll reply as soon as possible.
