I think it's important to keep track of exactly how much your bridesmaids are shelling out for the wedding. It can really add up.
For me personally, my girls are only paying for their dresses and shoes and I paid a contribution to the price of each dress to absorb some of the cost for alterations.
I have been a bridesmaid both in weddings where the bride has asked that we pay for makeup/hair and where she hasn't. I have elected to pay for the makeup and hair of my girls. I think this also makes it easier for me to decide the style of hair/makeup they wear.
I think flowers are really a grey area. I certainly wouldn't feel comfortable asking my girls to pay for those as I'd class them as part of the wedding styling and my responsibility.
Hope this helps!