Which of the following is not considered a proper roofing material?

Bitumen membrane is a type of roofing material that is primarily known for its use in flat roofing systems and is typically composed of asphalt or modified bitumen. While it serves specific roofing purposes, in the context of this question, it is often seen as less conventional compared to the other materials listed.

Metal shingles, asphalt shingles, and clay tiles are all traditional roofing materials that are widely recognized for their durability, aesthetic appeal, and effectiveness in protecting structures from the elements. Metal shingles can be lightweight and long-lasting, asphalt shingles are known for their affordability and ease of installation, and clay tiles are praised for their longevity and distinctive appearance.

When categorizing roofing materials, it's important to consider industry standards and typical applications. The question appears to focus on the most common roofing types used in residential settings, which elevates the other options over bitumen membrane as a primary roofing material. Understanding the context of each type of material helps differentiate their appropriate applications in various roofing scenarios.