Help-Lowering the roof

[iambennu]

I am rebuilding my home that was destroyed by Katrina and I am almost finished with the "before" layout, but I do not know how to lower the roof.

I am using Home Designer Suite 7

The south and north facing walls in the house onl come up to the waist about 4 ft. How do I do it?

Can I just lower the roof and have it cut off the walls?

Thanks in advance,

iam