Porch Walls - HELP!

I'm having trouble drawing some walls for around a front porch.

I am adding a front porch onto a house. It will be 18' left to right and 8' front to back. It is 7" below the house main level; you have to step up 7" to go into the house. The porch floor surface is 12" above ground level. The left and right sides of the porch AND the left hand 12 feet of the front side have 12" thick walls that DO NOT sit on top of the porch floor; but they do sit on the ground and extend 23" above the porch floor. Thus the total wall height is 37". These walls are taking the place of railings. The wall have the same 8" o.c. vertical siding that is on the house. The porch will have a simple slope roof on it. The roof will be supported by three posts that sit on top of the 12" thick wood siding walls.

Now for the final detail. The front wall is 12 feet long. The center 7' of the wall drops down 6".

What Home Designer Pro 9.0 structure tool option(s) do I use to get the effects I am speaking of above? How do I control the height of the walls and then the drop down section? The walls DO NOT have a foundation. The walls are simply part of the treated lumber structure of the entire porch. There is 3-1/2" T&G flooring.

I hope this is all clear enough to understand. If it is please help me; it's driving me up the wall! Pun intended.

Define your porch using invisible walls in order to get your roof built. Then use appropriately sized soffits (or slabs) for your visible porch walls. You'll have to butt the soffits against the invisible walls, and manually place your posts. Using either soffits or slabs will provide you with the flexibility to place them without regard to the room specification dialog.

Hope this helps. :)