Below are links to experiments with various aspects you could investigate in conjunction with the green roof project. Some of these have been done by other educators as more of a project than a simple 45 minute lab.

Effect of Color
https://www.vernier.com/innovate/roof-color/

Insulation
https://www.vernier.com/experiments/msv/9/good_sock/
This can be augmented with:
https://www.vernier.com/innovate/interior-and-exterior-temperatures-with-and-without-insulation/

Temperature at different depths
https://www.vernier.com/experiments/esv/9/soil_temperature/

Photosynthesis of plants
https://www.vernier.com/experiments/bwv/31c/photosynthesis_and_respiration_co2_and_o2/

Soil as a natural filtration
https://www.vernier.com/innovate/two-liter-creek/

Biodiversity (inquiry-based)
https://www.vernier.com/experiments/esi/15/biodiversity_in_ecosystems/

Soil Moisture
https://www.vernier.com/experiments/awv/11/soil_moisture/

Example shopping list:
https://www.vernier.com/cart/share/85925103216102497

Related:
What do I need to do to prepare for outdoor data collection?