A home is hardly a shelter without a roof. This covering for a home is one of the primary defenses against the elements. Rain, snow, wind, and sun are all kept out out and, in the case of rain, diverted by the gutters away from the house.
The surface of a roof is made up of shingles that may be metal, asphalt, ceramic, or another material. The structure is built on pitch to help funnel precipitation to the gutters. Water will travel along the gutters, through the downspout, and to a drain. This drainage systems helps prevent water from pooling around the base of a house and reduce erosion.
Roofs also help with the insulation of a home. In hotter regions the materials used are good at reflecting heat from the sun. For colder regions the insulation keeps heat inside the house for better energy efficiency and to prevent ice damming (i.e. commonly seen as icicles).
Roofs take a lot of wear and tear from the weather. The most common problems are damaged shingles, leaks, clogged gutters, and ice damming. Ice damming occurs when snow melts, runs down the roof, and gets trapped under more snow or debris. The water refreezes and can potentially damage shingles or the gutter.
For this task it is best to attach a brush to the end of pole to clean the shingles. It is safer than climbing around the roof. Do not use a pressure washer as an alternative. It can damage the roof and put water up under the shingles.
You will want to cover the plants below with plastic to protect them from the bleach. If plastic is not an option, heavily water down your plants before and after the task. The water will help to dilute the bleach.
References: 1 - Wikipedia