Flat Warm Roof Joist Detail

[koracer]

I'm in the process of building a Brick & Block studio in my garden, I've come up with a couple of design options for the warm roof/joist layout.

Ideally I'd like to keep the thickness of visible roof as low as possible.  In the images below, option A is my preferred, but googling hasn't led me to much helpful information.

 

Option A is bricked up to the lower OSB roof board level, 7x2 bonded/nolted around the perimeter of internal blockwork and joist hangers user to attach the joists so the top of the bricks and joists are the same level.  I can see getting the fall angle may be a little bit of work, lots of cutting bricks.  I'm also under of how I'd seal the OSB to the brickwork, it would be attached to the roof joists, but then nothing for 300mm of the wall.

 

Option B is typical of what I've found when searching, Joists on Top plate, overhanging the walls.  This makes the roof much thicker externally as there's 7" of joist to show as well as the warm roof.

 

Could anyone offer any advice, is option A a bad idea?