Roofing material is a potential groundwater contaminate. If you choose to grow food near your house, I would suggest these roofing options: wood shakes, clay tiles, earth or thatch. As for metal, the best option would probably be stainless steel or another metal painted with a non-toxic paint.
Wood shakes are derived from rot-resistant tress like Redwood and Cedar. These trees contain alleopathic chemicals that seek to inhibit the growth of other living organisms. Rainwater run-off may challenge the growth of plants near the house. In my experience, I haven't observed noticeable differences in plant growth rate around redwood or cedar trees or boxes. The life-expectancy of a cedar roof is often between 30-40 years. If the shakes are treated and sealed, this can prolong their life. Consider the use of a
silicone seal to waterproof the shakes.
Clay tiles can last more than 50 years. They are heavier than most other roofing systems and can require extra structural support in the house and roof framing.
Asphalt shingles are a petroleum-based product and a major source of pollution in rainwater runoff. It's horrifying to read the small print on some of these roofing packages that are asphalt based.
Most
metal, corrugated-type roofing is galvanized, meaning that it has a thin coating of zinc. Zinc readily leaches in rain water and will contaminate the soil surrounding the house. Painting the metal roof can help prevent leaching. A stainless steel roof is probably a better option, but it will still leach metals such as Chromium, Iron and Nickel. Copper roofs can be beautiful but they are very expensive. Some copper
sheeting is really lead with a copper coating, so be clear on what you
are purchasing. Copper will leach in rainwater runoff, too.
References:
Rooftop Runoff
Pollution Prevention and Stormwater
Leaching of Heavy Metals from Stainless Steel
