I've been meaning to draw up some templates for making paper wagons for the Peco chassis for a while as its a great way to knock up all kinds of fun wagons, and if you overlay the strapping with black painted plasticard etc can look really good.
This one is just a paper build on a Peco 10ft chassis
If you want to make your own then the artwork is below, print at 600dpi and have fun. The tiff one is the best quality and most likely going to just print right, the jpeg is there too just in case.
For OO you'll need to resize it. I don't know what the dimensions of the OO chassis are so you'll have to work it out
Print on nice stiff quality paper (the one above is on cheap paper as tester) and make the folds sharp. Fold up and glue (for laser print titebond woodglue is awesome for this, for inkjet you need more care but spraying the back of the sheet with spray mount might well do the trick).
Cut out four of the corner bits and wrap them round the corner to hold it together.