Even older than the asphalt shingle style are wood shake shingles. They last even longer than composition shingles. Wood is a more natural and softer look. Although they are made from trees, they are friendly in that they decompose unlike petroleum products. If well maintained they will last a long time, but wood shake is always a fire hazard.
Metal roofs are popular with those trying to save money on energy bills. Metal roofs make you save money on air conditioning bills because they reflect money in hot environments. If you choose a painted roof, you need to have periodic painting maintenance. However metal roofs last a long time, and do not need Denver roof repairs very often. Metal also does a good job of protecting your home from weather.
An older and environmentally friendly roofing material is tile. Tile is made of clay or sometimes concrete. These are naturally fire resistant materials. Clay is just earth, so it has no problems with decomposition. The main drawbacks of tile and concrete is that these are heavy, brittle materials. They provide good protection, but are liable to break and need a solid roof to support the heavy weight of these roofing materials.
Flat roofs have completely different roofing materials. Some are basically a giant asphalt shingle. It uses hot asphalt inlaid with stone. These are not very friendly because they use a large amount of smelly tar, which is a risk to installers as well as the environment.
Eco roofs that use soil on the top are very good for carbon consumption and global warming. They can basically have a garden on your roof that also provides insulation. Engineered rubber roofing is made of recycled materials but may be hard to find from your Denver roof repairs company.