Sedum pulchellum ‘Sea Star’ a gob smacking flower,  frost hardy down to -2 or 3, so may need some protection, and self seeds quite happily 
 
Sedum is perfect for ground cover, roof projects, wheelie bin hutch roofs etc.
(We can also create bespoke structures, get in touch to discuss your needs).
 
Plugs provide a versatile solution to providing coverage and will grow in both horizontal and vertical locations. These plugs are designed for you to plant yourself on your prepared roof , approx 20-25 plugs per sq mtr.