When photographing buildings – if your aim is not an artistic presentation but the exact reproduction of a view – it is rather important for the perspective to be the same in the picture as in real life. The wide-angle lens of your camera makes this difficult as it strangely tilts buildings backward. This perspective distortion can be easily corrected as described in the following photoshop tutorial.
First of all, take a good look of the photo and decide what kind of perspective correction you need. In the sample picture, the building tilts backward and a bit to the right.
In order to define horizontal and vertical more easily, put Guide Lines onto the image. Click the Ruler on the sides of the image window, and drag onto the picture. If you cannot see the ruler, turn it on by pressing Ctrl+R. Drag the upper (horizontal) ruler for horizontal guidelines and the side (vertical) ruler for vertical ones. You should align the vertical guidelines with the sides of the building’s base, and the horizontal ones with any line in the picture that you wish to make horizontal (e.g. roof edges). Click View/Clear Guides to clear misplaced guidelines.
Press Ctrl+A to select the whole image and Ctrl+T to select Free Transform.
Note: Photoshop also contains a Perspective feature (under Edit/Transform/Perspective) for this purpose but Free Transform provides much more options.
Free Transform draws a border around the picture, with handles on the corners and midpoints. In the Navigator window, shrink the picture until it fits well in the middle of the screen. By dragging the handles of the upper corners, pull them until the edges of the building get parallel with the guidelines. You can drag all handles freely to transform the image as you like. When performing perspective correction, the lower handles are rarely needed.
If you got the building straight, press Enter to make Photoshop render the image anew and make your changes effective. Click View/Clear Guides to clear the guidelines and behold the result: