Hi mate
ive attached some pics below to explain what it is from the inside
basically I built a wooden cable duct which goes from one side of the wall to the other which is that boxing you see on the top edge of the wall/ceiling
behind that is another long piece of chipboard and behind that is what I believe to be the wall plate which I think is two 2x4 timbers
So these would strap the joists to the brick work around the windows for the rafters to sit on
rafters are 6x2, it’s a lean to roof with a gradual slope
I’ve also attached another picture of my Upvc door and above the door is a timber which I’m assuming is the wall plate which goes all the way length wise across the front wall
I don’t think adding a lintel is possible due to lack of clearance, unless the wall plate suffices