Structures: Determine if you need to add terraces, walls, fences, pathways, arbors, ponds, benches, decks, patios, stairways, planters, arches, lighting, edging, etc. If you are working with a steep hill, you may want to incorporate terraces to graduate the incline. You may need to construct a wall to block off an area. Fences are great for vines. Pathways add an invitation to the garden.
Materials: You can use wood, stone, rock, mulch, brick, driftwood,etc. Observe your existing features and determine what kind of materials 
would go well with what you already have. In some cases one particular material may be all you can use. Consider pro’s and con’s of each type of material (longevity, maintenance, safeness, etc.) and decide which will work best in your landscape.
