Thanks for the helpful suggestions.
I started at the bottom (twice!), and I now have a reasonable model of my house (after 12 hours solid 'work').
However, because of the half basement, half of my house is 'floating' above 'ground level' (actually basement floor level). How can I fill in the missing earth?

Thanks again,

Steve

I want to model my house which is built on a slope which falls away to the rear of the house.
Consequently, the house is 2 storeys at the front, but 3 storeys at the rear. The rear has a basement which only extends half way towards the front of the house.
Should I start 'building' the house at basement level, or at main floor level and 'add' a basement below?

Thanks,

Steve