I'm crazy about zoysia tenuifolia. How would this work out as an alternative to cedum on a green roof? Would the whole structure have to carry a heavier load as a result of deploying it compared to cedum?

I'm not familiar with your climate zone and I don't know zoysia. I do know about echeverias though and find them tougher and faster growing than sedums.
The hybrid cultivar known as 'hens and chickens' would work brilliantly on a green roof. The flowers are gorgeous.

I'm totally with cercis on this one. I've been dreaming of a green roof on the s-CONo2 series. I want to build one of these in Port Aransas (which is my home town on the Texas Gulf coast). Sedums, echevarias and most other succulents do VERY well in that climate. Succulents do VERY well in Central Texas' climate as well. In fact the succulent/xeri-scaping garden thing has really taken root here. It seems everywhere I look I see a new garden, but I never see one on a roof.

Mark