Before you get started, think about the kind of garden you want. Is it a serene place where you can find solitary respite, or a spot to entertain? The space itself will help dictate what you can pull off. If your vision includes a swimming pool, putting green or something else that's complex, it's best to hire a landscape architect. Professionals aren't just savvy about selecting plants that meet your tastes and budget -- they also know other important stuff, like local building codes, projected costs and how much weight your roof can stand. Landscape architects will start by scouting the site to assess the roof's age and its overall condition. If you have a homeowners' association board (HOA), your landscape architect will develop and present a design to the board for approval. Remember: This pro is working on your dime, so make sure your vision gets realized in the final plans!