yous see that some of the faces are white, and some are blue, that is really going to mess up pepakura. i do alot of sketchup so some thips are
make it in google sketcup 8, but export it back to version 6 to be turned into a pep file
if you highlight the blue faces, right click and select "reverse faces" it will turn them white (its just that they are the wrong way round and pepakura dont like that)
keep going. alot of people hate google sketchup as its not a "real" 3D modeler. i doisagrre, i have done some epic stuff in sketchup.
finnally, plugins, these are like mods that mean that you can do different things, some are free, most are paid for