I'm starting to think you're trolling me. I understand:
- pitched main roof
- flat deck roof
- metal transition
What I've asked repeatedly is
- which eave is higher the main roof or the flat roof
- which way does the 'flashing' drain, in the 4ft or 20ft direction
- what (again) supports the 'flashing'
Also, why not obviate the material compatibility issue by putting in a 4x20ft skylight?
And a gutter, if the main roof washes over the flat roof it will degrade the life of the flat roof. Good thing it's membrane. Make sure it's flat or you'll have standing water in puddles.