[Cob] any ideas for building cob on a hill?

[greg]

There's a property that my wife and i really like but the problem is
that the only place to build on goes from 10 degree slope down for
about 20-25ft. Then it drops off on 30-40 degree slope down for
a long way.

My questions are:
how deep should one dig into the land to get a level
space versus using fill dirt to get a level space?

what precautions should be done to stablize the soil
downhill of the house so that it doesn't wash away,
taking our proposed beautiful cob house with it?

with keeping water away from the cob and a slope going
down to it, any ideas for water flow to keep the water from
running right into the house in a rain storm?

are there any considerations for building on a hill that i should
be concerned with?

thx
greg