Joist supports for a new flat roof on my lock-up garage.

[BungalowBill]

I need to replace my corrugated asbestos garage roof which slopes from the front to the back. There are currently only 2 rusted angle iron supports in addition to the front support (door frame) and the back support (wall) so I intend to replace these with wood and add a few more to stop the new roof sagging.
I expected to use joist hangers but the tops of the walls are very rough and uneven brickwork. I can't repair this without disturbing the neighbouring garage roofs which are old, fragile asbestos sheets.
So, will it be satisfactory to use joist hangers but screw them onto the brickwork or could I do something better?

 

[noseall]

it depends upon how you want to finish or cover the roof. if you are simply going like for like, i.e. corrugated sheeting then you will need to build in purlins, at pre-designated distances along the length of the garage.

if you are going to ply & felt, then you could build-in say three purlins, one at the front, one middle and one at the back. then fill in between these purlins with adequate sized rafters.

....or you could simply build-in joists all the way down.

joist hangers, even on a bearer plate, are not suitable so near to the top of the wall. there simply isn't enough strength and weight of masonry.

 

[BungalowBill]

Thanks noseall.
I will be replacing with corrugated cement sheets. The walls are single brick so I'll have to get access to the adjacent garages to build in purlins or joists.