Large scale fiberglass project

what kind of difficulty would I be looking at to make a fiberglass rear hatch on a 240sx. How would i make a mold that big, and basically, what would I do to do something on such a large scale.

Also, how hard would it be to do a hood in fiberglass?

Are you asking about the hatch itself, or the area inside?  Basically you need to mask off the surrounding areas (you can use masking tape and trash bags), and apply some type of mold release (car wax, aluminum foil, etc.).  Cut plenty of strips of fiberglass mat, and have at it.  If you're doing the inside of the hatch area (spare tire area, etc.), you'll want to place some sort of border in the middle (strips of wood) so you can make the mold in multiple pieces.  This is so you can remove it if necessary.

I wouldn't attempt a hood unless I felt 100% confident in my abilities first.  Trust me, my first attempt at fiberglass (and bodywork) was front fenders and a header panel for my car.  The header panel I had to make from scratch, since mine was missing.  I was doing a headlight conversion, and needed to make room for the lights, and try to blend it all together.  Almost six months later, I'm not done, but it's looking much better.  Getting the shape of a hood is not going to be the problem.  The problem will be with getting the mouting points and latching components correct, all the while making it plenty strong, yet lightweight- all at the same time.

Yeah, I am talking the actual hatch. I was thinking about using aluminum(very thin, from aircraft supply place)  for the hood, with a fiberglass under skeloton for sturdy ness.

Would normal car wax work as the release agent? Is there a special, extra thick, wax I can buy. I am very new to using molds with fiberglass, and I  really appreciate the advice fellas.

oh, and as far as laying the matting down over the hatch, are you talking about making the mold like that? Can I use normal fiberglass matting and resin for the mold, and then cast the actual part from that?