A few years ago I used data loggers to measure temperature differences between my green roofed attic and my neighbors asphalt attic.
Several friends of mine work in energy efficiency and recommended HOBO data loggers. They’re amazing and inexpensive. I set mine to measure temperature hourly for several months.
The results were good. The green roof attic was on average 26 degrees (F) cooler. The ‘blip’ in the data in early June was a rainy day.