As far as I know this is a fairly common practice in the card modelling world, I plan to do it myself as I recently purchased a 1:48 model I would like to build at 1:24.
As long as you are only building one copy I don't see a problem with it. We have a similar law in Australia regarding video games and audio/movie DVD's... we are allowed to burn a copy of items we own the original disc of in order to preserve the original. It comes in handy when you have kids who have no idea how to look after a DVD disc.