You would want to make your own function.
On the bottom of the event sheet click on 'Add' (NOT Add Event) then select add function.
Inside the function you would create all your objects.
Each Time that function needs to happen you simply call it.
Let's say:
I have a square room and a door on the top center for my starting map. Once I walk into the door my character is at the bottom center of a new blank page - this is where my function would be called. I would create an exit right where my character is - and the next time I walk into it that will bring me to my previous screen. Create a random amount of enemy objects and place them randomly around the map. Set there stats based on hero level or room level. Create atleast 1 random door to move deeper. Randomly place that on an edge of the screen.
Now each time I bump into a new room door I will create a new but also random room, and I can walk back to my previous rooms.
It will be a lot of work to get the base down, but once you have it where you want it you can scale it infinitely