TPO – This roof is heat welded, slippery when wet, best in non traffic areas on flat and low slope roofs, not as much shrinkage as a rubber roof, more labor intensive so more expensive, probably the second most durable as long as no traffic.
PVC Single-Ply Membrane – Exact same process as TPO but different materials. The different materials do not make it much different in price. Also a flat to low slope roof, not as much shrinkage as rubber and more labor intensive than rubber. Durable as long as no traffic. Slippery when wet.
Modified bitumen - No to low traffic. Tears and punctures under too much traffic and is sticky when hot. Flat and low slope roof. Absorbs heat. Dollar for dollar a little cheaper than the previous two.
Built Up Roofing (BUR) – Build up is usually a commercial roof because of the expense. It is material and labor intensive. For flat and low slope roofs. Traffic durable.
Metal is a higher maintenance material that needs coating usually every three to five years depending on weather variables. It is not safe to walk on when wet. Best on medium to high slope roof. Initially comes in a variety of colors but to maintain those colors can become quite expensive. Most people simply cover with silver coat during maintenance phase.