If your ceiling is water stained, it's a safe bet you have either a roof leak or a condensation problem. It's important to figure out what type of stain you have before you repair your ceiling.
Fortunately, these stains are easy to identify. The condensation stain is usually found on a ceiling panel near an exterior wall, often in a corner. Instead of one large stain, you'll see several smaller circles of stains. These stains vary in size and shape, but they tend to have white centers. Condensation stains appear even if there has not been a rainstorm.
The rain leak stain can be found anywhere on your ceiling: near an exterior wall, surrounding a ceiling fixture, around a ventilation pipe or even in the center of the ceiling. This stain tends to be concentric rings that get progressively lighter as they move outward. The center stain is dark, because it is the oldest stain. Each "ring" by the way, is a separate occurrence. If you see lots of rings surrounding the dark stain in the middle, you know the roof leak has been around for quite some time.