I would think that you would want to work and 'try' to make money with a B.Arch. A masters in sustainability is not going to do a damn thing other than increase you debt. Just so you know, no one really cares about that crap.

^  DeTwan is right.  It's little more than a marketing slogan.  Save your money.

listen to the two above posters.

you can learn that "sustainable architecture" yourself. 

really.

go save your money and just work or go into real estate.

what IS sustainable architecture, growing corn on the roof?

Wow, jaded posters.  Having a degree in sustainability can open up other job opportunities related to the built environment but not directly architecture.  It really depends why you want to do the course in terms of deciding if it's the right thing for you or not.

Are you looking in the US?  I would have thought an MArch was an accredited course and a MS is not.  However, with the BArch, it shouldn't matter for licensure if your master's is accredited or not.

So you know, there are a number of architecture and sustainability master's courses in the UK which tend to be cheaper then US ones and are one year compared to two.  If you are interested in progressing your sustainability knowledge and wanting to spend a bit less, you might consider looking into some of those as another option.

Best of luck.