How do i create maps like Fortnite?
Hi @meowmeowbowow! Welcome to the Forums!
Maps like Fortnite and other AAA games all come down to level design and planning. It takes a good amount of practice but it is a great skill set to have.
Here is an Epic Games learning course on level design fundamentals that will teach you how to block out and plan levels, which is the starting point of what you are going to need:
I hope the above course provides what you need!