I'm hoping someone can give me some advice about fondant roses. 

I am making wedding cupcakes in August and the customer is wanting a rose, daisies and leaves on the tops of all her cupcakes. I'm wondering how early I should start working on them? I usually work with gumpaste for cakes and wait for the gumpaste to dry before putting on the cake. 

The other question I have is should the fondant roses harden before I put them on the cupcakes? Or if I were to start on them soon, if i store them away would they harden or stay slightly soft?

Fondant alone never really gets hard.  You can make them way ahead of time and they will stiffen.  If you are going to store them I would use a cardboard box which will absorb humidity.

If you add tylose or cornstarch they will harden crispy. You can make them as far ahead as you have time. If you want them hard store them in cardboard boxes. If you want them to stay soft you could store them in airtight plastic boxes or use modeling chocolate.