It's supporting a flat roof only?
What kind of roofing?
What is the rafter length on each side of the beam?
Is the flat roof portion now enclosed by the trusses? So the flat is no longer a roof, but is interior?
The trusses are not counting on this wall for support? Correct?
What is the length of the rafters (perpendicular to the beam) on each side of this wall?
Do you know how thick the layer of gravel is?
I will assume 1" thickness
I will assume 1" for the analysis.
5.25" x 11.875" 2.0E LVL
That is the beam you need based on the assumptions stated. You can plan for a 4x4 doug-fir no. 1 for the posts.
If the beam is spanning the 14' you stated, then only at the ends.
No problem. I'm happy to help. Good luck with your project.