Hmm, what is going on at BioWare? Great question, Shepard.
Allow me to answer for you.
I googled Bioware to figure out how to draw their Edmonton office, aren't you proud of me?
A true piece of Mass Effect History: just after Mass Effect 3 was released, BioWare put out an app for iPad called Mass Effect: The Final Hours. It was a bunch of behind the scenes stuff.
In that app, they scanned in the one page (really) document that detailed their plan for the ending. According to BioWare themselves, this was their planning document. It's in two pieces because on the iPad, you'd have to scroll.