i use the Railing Tool for my barge/ridge capping for my roofs. i use a custom profile, have it associate to the Rail & have the Rail Tool snap to the corners of a roof.
i do the same with my concrete kerbs. i have my hardstand / driveways modelled with meshes & i have a custom profile for the kerb shape & have the Rail Tool link to the mesh corner.
i just tried it with the wall & i think it only associates to the bottom of the wall. the workaround here is to increase the bottom offset of the rail to match the wall. it's not clean, but it's associated.