they both have advantages and disadvantages.
advantages for alum is it's stronger, less visable, lasts longer.
advantages for fiberglass, it doesn't dent, easier to wire the frame, and cheaper.
I learned how to wire screen frames with aluminum. so it's a piece of cake for me to do either. the mastery comes with experience. it's not something everyone can do for sure.
I can whipp out a new screen patio door in 3 min. I have a table I made for doing this.
it's 3" styrofoam with 1/16" alum skin on both sides. I cut it to 8'L X 2' W. I made 2 of these. and set them on a set of sawhorses with 4' wide 2X6 screwed to the sawhorses.
with this I can adjust for the width. I do them on location. window screens(1/2 screen/1/2 the window) are $15 full length screen in windows and patio doors are $35. that's how much the glass shops around here charge. fiberglass or alum. doesn't matter.
CR lawrence is a good place to get screen parts from (corners, springs, hardware, and spline etc)
C.R. Laurence Co., Inc.
I recommend this brand of screen rollers,
you can get phifer wire products at home depot.(the actual screen material)