Are you thinking of using fiberglass just to form it out then maybe an aluminum roof? The entire thing out of fiberglass?
Either is doable but I promise you what you save in money you'll spend in labor 2x. As long as you're a DIY kinda guy and don't mind spending a lot of time on it!
I don't know of a specific how-to on building a roof but the concepts would be the same as for a fiberglass rack enclosure. Felt, fiberglass & resin, a helper and some time. If I were going to undertake a complete glass roof, I would make it in two pieces and glass them together.
I suppose you could use wood but I can't see that ending up looking very clean.
Im build 2 aluminum roofs for the maverick. I built one for my last commander. I take a piece of wood and build a pattern that forms against the cage. take it to a sheetmetal shop n have them brake it. I build the boxes that hold the radio and speakers in it along w all my switches for anything thats mounted to the roof.( lightbars strobe dome lights radio switch) then weld it to the underside of the roof. The one thats going on my maverick is getting a 500 watt amp 2 8" speakers 2 6.5" speakers fuse block radio strobe lights front and rear light bars side lights and dome lights. Ill try n post pics when I get done w it. I use stainless steel clamps w rubber to mount it to the roll cage. Lots of work but when finished its a one off roof that nobody has. Most important thing when building one is keep everything high. If your a crazy driver ppl tend to hit there heads up top then put their seatbelts on!