Help! Whats wrong with my roses?

it sounds like mildew.  Some rose varieties are more susceptible than others. Good ventilation around your plant is a good idea as is a mulch of manure etc.  I think mildew is worse in hot, dry conditions combined with lack of ventilation if your rose is against a wall etc which mine limit air flow round it

I'd google what to do for mildew on roses as I'm no expert