The Space and Wall tools are great for concept design and space planning! I generally start with Spaces first. Then l trace the Space Boundaries with Walls. The walls are Center justified. Would it be possible to generate Walls from Space Boundaries? Something similar when you right click on the Walls tool in the Tool Palette, and select "Apply Tool Properties to Linework". But instead of linework, it can pick a Space Boundary.
First, what you call Space Boundaries are not such. It's just like a polyline. You have drawn non-associative spaces. Space boundaries are are walls, etc, that bound an associative space. See this help topic to make a space associative. This method requires you to place walls around the space first. You could program a solution to select a space and then place walls around it, but it would get difficult if there are other spaces next to the one you select. Will the walls also be a boundary for those spaces? Of course, you need to first learn to program.
