I’ve never actually made something so large, so I don’t exactly know the solution. I’ve built a large cathedral resembling Notre Dame and there is a weird lighting glitch that happens at the top of the Nave:
Is it going to be an all interior map (without anyone going/seeing outside of it?), if so, I’d recommend placing a large (20+ stud brick) ontop of the place so everything below it is dark and you could add lighting).
If players will be able to see the outside, I recommend altering the ambient, found in lighting to 0,0,0 so the whole environment would be dark.
If its only the interior you can even place individual lighting outside, aimed downward and move it around until it blends the way you want. Its more of a cheap fix compared to playing around with the ambient but it’s just as effective if you do it correctly.