I don't know anything about Blender either, but is there no way to set physical dimensions?
Or, if it would be a sort of "freehand sculpture", without any reference to dimensions, maybe he could create a little cube next to it, and give that cube exact physical dimensions?
Since people can design planes exactly to scale in Blender, something like this should be possible.
I have zero Blender know-how but maybe something like this? http://www.shapeways.com/tutorials/exporting-from-blender
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