Fiberglass or Steel Rod???

Hello all
I'm finally ready, after years of paying for houses, kids, honey do lists, on and on to build a street rod the way I want it. Not looking to rat rod.
My question to the experienced here is what is the advantages (or disadvanges) of a fiberglass car over a steel car. And is it nessasary to use a custom frame for a higher HP engine?
Plan on conventional front suspension. It seems I'm having trouble finding a steel one solid enough to start with that's not crazy priced.

P.S. I have a nice 1999 GT I thinking about using as trade material. Yeah, I know that's not going to get me very far. :CRY:


Thanks

Steve