Looks like creeping phlox, but apparently is Trailing Rosemary? One pinner said: Trailing Rosemary produces beautiful blue foliage. It requires little water, and has a moderate growth rate. It has no allergens, but yet is very fragrant.
Hardy succulents like sedums, semperveriums, and ice plants are ideal for roof gardens, they require little soil and water, and can take long periods with not much watering.this would be really pretty as a roof to a chicken coop