I always tried with CTRL which is the "GUI" way for selecting single elements, SHIFT is normally for consecutive elements (think file manager). But I'll try it with SHIFT.

Still a list of walls would help a lot to quickly select a wall e.g. if it is out of view or very small to hit with the mouse or to select walls that are not next to each other or to check several pieces if the coordinates/sizes match up etc.

Thanks