Do you mean the flowers themselves have brown spots on the petals? If so this is due to rain or overhead sprinkling. Just pull off the brown petals and wait for the weather to change. If you mean brown spots on the leaves, I would need to see a photo to determine if it is a rust disease or black spot disease. The first line of defense is to pull off infected leaves to keep this fungal infection from spreading. Try to keep leaves dry and remove any plants that crowd the roses and block air circulation. Any fungicide spray listed for black spot will help to control this fungus among us. Keep growing, Marianne Binetti