Is it possible to add an option to edit lenght of each side of the wall then? I think that in that case it would be possible to achieve what OP wants. Btw I suffer from that too:(

As for your workaround... Yes, it is possible to do this way but if I will change thickness of the wall after drawing walls around the room, drawing becomes inacurate, part of the wall gets placed on the room and if I want to reposition wall, it is very hard to do because there is no option to snap these walls to existing room:( Or am I missing something?