This is general question come into mind after doing B Arch. It totally depends upon your aptitude towards architecture along with your willingness to pursue design as a career.
To gain niche experience in the field of Architecture and stick to a particular genre or specialization, then M.Arch or Ph.d would be better option.
Many students who were unable to pursue B.Arch from prestigious institutes like CEPT, SPA or JJ College of Architecture, can aim to do a Masters or Ph.d from such colleges, to gain knowledge and exposure from the best of the architectural world.
An MBA will not be very useful for architecture compared to M. Arch unless you are going to do business instead of professional practice of architecture.
B. Arch and MBA, both are unrelated. Its a different profession. Architecture is not a business but a profession.
If you are looking to practise under a senior/principal architect and later plan to start on your own, then M.Arch followed by an executive MBA would help; since the later would demand finance and business development knowledge as well.
An MBA would be beneficial to an Architect when he/she in a Senior/Partner position. Apart from M.Arch, one can also explore M.Plan and M.Tech in Urban Infrastructure Management.