@hollietruesdale - The picture I posted before is a sedum (a succulent ground cover) mix, with accent perennials. This roof was installed on a new Boise State University building. Depending on your area, a wide variety of ground cover and accent plants may be available to you (depending on your substrate depth...<6 is called Extensive, >6 is called Intensive). Retrofit jobs are common, as long as an architect or building engineer OKs your roof weight load rating. If you are building a new house, You Architect can sole spec a green roof company. In our case, we typically travel with our fully grown roofs to the building site and certify either a landscaping team or a team put together by the GC (sometimes the owners opt to install themselves) for installation. If you are interested, check out LiveRoof.com to see if a grower is in your area. Otherwise there are many options available to you!