This is a full set of .STL files for the ArduCopter Quad frame and a mostly complete set of DXF files. There was a user on a DIY Drones Post offering up the open source files in any format. I simply asked for .STL. The DXF set was from a user that made a carbon fiber frame.
I have printed the entire STL set in ABS plastic on a Makerbot. It feels a bit flimsy for flight ... however after screwing that main plates together against the arms it seems reasonable.