Wow, that could be one of the many California bungalows we have here in the historic district of Orange.
I have helped people use this space before as additional living area. Not an easy process though.
If you are in a historic district you have to design the exterior to their standards and even then you have a long way to go to make the area code compliant for living space.
You have to think about the stairs to get to the space, the emergency egress, the insulation, how to condition the space and many other things before getting to the structural aspects.
In short, you should get approvals from your planning and Building departments first.