If there is going to be rainwater harvesting:

• “Green / grass” roofs may mean little roof water run-off.
• It seems that people tend to either go for a Grey Water recycling or a Rain Water harvesting system, not both. Have to cost these both up.

Anyway, if there is going to be a rainwater harvesting system, it would seem that putting the storage tanks for this on the west side of the house could be ideal.

• This side of the house should have little if any people traffic.
• The roofs could all be sloped to drain to the west so that the drain pipes could flow down to a single rain water harvesting tank.