Tools that can be used now is booleans and sweeps. You can have a polyline and then somewhere a rectang profile with the dims of the wall and make a sweep (Michael should correct that problems with the corners first). If it is a simple 1-2 room house you can use booleans for the rooms.
Making walls is not the difficult part. If we ask for walls, then we should ask for doors, windows, floors, railings, etc. All these can be modeled with boxes, sweeps, booleans etc. So, what we basically asking is a set of architectural commands and not the ability to make the architectural model because this can be done already. Also, from my experience (>15 years in building models) the changes will be so many that there has to be a fully editable modeling history.
So before Michael gives us commands or even a small plugin to speed up the wall drawing, he has to finish the object editing and grouping and the history editing.