I'm thinking of what to use for the body panels on my car. The only thing I can think of that would be really feasible is plastic cut and bolted on. This doesn't seem very light or aerodynamic. Does anyone have any other ideas about how to cover my frame?

We used coroplast for a body. It is corogated plastic. Very light and easy to cut with a knife if you want. The entire body weighed in at 5 pounds.

I moved this into the body section. I have seen numerous materials used for the body. Plastic works well, the plastic cardboard works great. Sheet metal can be formed and riveted on. Fiberglass bodies can be some of the best looking (or worst, seen them too) cars out there.

We have used aluminum coil stock and fiberglass and combination of both.

Check out Home Depot or Lowes.
In the roofing section they have aluminum roof flashing.  It comes in 10' or longer roles and 10 to 20" high and very thin. 
Easy to work with.

Vic 

Thanks, I'll check it out.

Composite body shell building
2 parts:
http://www.youtube.com/watch?v=_frFYZRecX8

Part 2 Competition:
http://www.youtube.com/watch?v=gLhASxFEFZY&feature=related

A lot of good info in these films for builders.   

I have currently been using the aluminum "kick panel" material sold at Lowe's and Home Depot. It is found in the area where the screen enclosure materials are sold. It's .025" thick, 16" wide, and 16 feet long for about $30. I use this because it becomes "stressed panels" on my cars (the body adds strength to the chassis). For something really light in a non-stressed application, I have used two layers of ordinary cotton muslin fabric saturated with polyester resin (fiberglass resin). It's fairly strong and it's waterproof, but much lighter than conventional fiberglass.