I have used the roof from the 3MM Society 'B' Set kit.
This is the right length and roof profile so rather than cutting another Worsley extruded aluminium one it seemed easier.
The roof was glued on using Evo-stick when still wet. It seems to have adhered rather well and it is square and contacts the body all round.
So, having found a drawing for a right hand version then the vents and rainstrips should be the same location wise but a mirror image.
The bogie etches are from 3SMR and the wheels are the latest Society offerings which have to be assembled.