I can help. What is the city and state so I can look at snow loading? What is the joist length on each side of the beam?
I apologize for the delay. I was away from my computer. I will provide a size for supporting the attic only and a size for support the attic and roof.
To support the roof and attic with 16' joists on each side and limit deflection to L/280 (about 1"), you need a 7" x 20" 2.2E LVL.
To support just the attic with the same deflection, you need a 5.25" x 18" 2.2E LVL.
If you're worried about headroom, yes.
For a steel beam, you can plan for a W12x45 ASTM A992 Gr. 50 to support the attic and roof with the same deflection criteria. The beam is 12" deep x 8" wide and weighs 45 pounds per foot.
You will need to detail the joists to brace the beam against lateral torsional buckling.