Hello, if the wall is transparent or the ground is empty (as well as the situation where doors and windows cannot be added to the wall), please check first:

1. Whether there is an unclosed wall in the space. If so, delete it and redraw it to be closed. If it is a section or a wall of different heights, we can draw the wall dividly,set it's type to half wall then you can set it's height dividly;

2. Check the wall transparency. It is recommended to set the "opacity" to 100%;