Creating indoor maps do i need to subtract space ?

If i wanna create an indoor level with the new engine, do i have to build everything wall by wall or is it done the old fashioned way like subtracting a room out of a vast space ?

Not exactly sure what the “old fashion” way is but you should be able to build it like any other level.

sorry thats really useless reply, its about whether you still supposed to subtract rooms out of space or now have to build wall by wall floor by floor in a lego style fashion

I believe that the more common way would be the “Lego” style.