green roofs and walls help insulate the building better. which conserves energy. it keeps it cool in the summer and warm in the winter. it also converts CO2 into O2 because the plants absorb the carbon.
people grow lawns, or plant shrubs, or have a garden.

After the tsunami, aid groups helped the rebuild effort by bundling together bamboo or some other type of vegetation and literally made houses out of them. They did put some sort of plaster or sheet board to protect from fire, and they actually were more flame resistant than houses here on the western side. Also, since they could be bundled so tightly, the "green walls" were ideal for insulation. The roofs, made of the same material, were built to curve up at the end to collect rainwater.

Also, they are 100% renewable.
I don’t know how they’d hold up as a multi story building, but i’m sure in combination with something stronger it’d do just fine.