@IDP hehe! u remind me of one of my lecturers,he used to say...the house of an african man is never complete until he dies...he will either add a bedroom,kitchen as the family expands...he he!
Anyway where is ur current house located? before you even seek architectural conseil you need to make sure that the zoning regulation of the neighbourhood allows for that change...from there tunaeza saidiana.
The Strong Do What They Want,The Weak Do What They Must!