That's one of the maddest projects I've ever heard of!
But usually that's a good thing.
I've taken a look around the internet and I couldn't find exact blueprints (only maps) but perhaps will help you a bit
link
(you can open it once you've downloaded google sketchup it's a 3d model of the cathedral)
And you could contact the cathedral, perhaps they can help you out, after all they want to get more people interested in the cathedral.
I'm really looking forward to what you make of this especially since I intend to build
this abbey in 28mm once I've finished the boards I'm working on now
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“People often claim to hunger for truth, but seldom like the taste when it's served up.”
My wip