I'm wondering if there are any big maps like one that was created for older versions called nuclear desert (or something similar)

If not, are there any limits at making scenes?

There's no real limit on the size of a scene, though the game will begin to act funky if you take it past a certain size. For example, I tested a 4000x4000 map and it would run smoothly, but occasionally jerk the animations. Reducing this number decreased the jerking, and I find the largest safe number I can use is any dimensions that come out to 6,000,000 pixels (i.e. 3000x2000).

Big maps with lots of terrain will lag badly.
No real limits.
Just complaints from others.