I'm under the impression you needed sketchup pro if you wanted to export to other formats- I don't imagine pepakura can read google's proprietary format. It costs $495...
I use AutoCAD for work and Blender on my own, and Blender is WAY faster for modeling objects, so long as precise measurements aren't important. There's ways to put measurements in there, but I don't think I would want to get into that judging by the tutorials. In any case, it's free, and after a couple tutorial vids (I like this guy
) you'll be up and running. Draw your concept on paper, model it in blender, then if you need to scale it you can figure out how to do it in Blender or you can export it to another program.
And if you need 12 decimal places of accuracy I'm really curious what you're modeling. Armor for bacteria?