Here's a couple other pros/cons
Fiberglass:
++Doesn't come "prepped" to mount on your vehicle. Often times you will have to drill holes in order to mount.
++Sometimes doesn't align correctly because of molding imperfections, requiring you to remove bracing and cut the fiber-panel and re-glass it to make it fit "Just Right"
++Doesn't rust obviously
++Lighter
Steel
++Big learning curve in working with sheetmetal. But it's tons of fun. I'm learning as I move forward...my truck probably won't be finished for 10 years, and chances are it's not going to be an award winning show-truck, but I'm LEARNING and that's the best part.
Hope this helped.