in a simple way see ( image 1 ) that showing name of layer syntax that should be in your Autocad files you send it to us and sure to get your result you are looking for
Image 1 Wall Layer Syntax
The walls are the same as you usually draw, but it is preferable that they be connected as much as possible, and of course the number of layers is according to the heights if they are uniform. see Example (image2)
Curves and lines must be joint as possible
Image 2 Example of wall Layer