Okay, I just checked the dictionary and realized there was no entry for flags; so I added Flags to the dream dictionary, I'm not sure if you'll be able to apply any of it to your dream or not but here is what it says :

Flags

A flag symbolizes the union between feminine and masculine. The pole is an obvious erect phallic symbol while at the same time the flag fabric itself represent the feminine, symbolizing the material of the mother and of woman. In dreams, as well as in waking life, the flag can also represent a totality; just as it represents all the men and women of a particular nation, in dreams it represents the inner life as a whole – emotions and creativity, attraction and power.

To dream that you are erecting a flag and planning it indicates that you are marking your virility and emotional progress. To lower a flag to half-mast symbolizes an inner sorrow; withdrawing into yourself as the material is folded up.