You can farm all of them around the map, but ensure you aim for the flashing circles when harvesting with your pickaxe to speed up the process.
In the battle royale mode, you want to make sure you have half an eye on building your stock of resources. In Fortnite, you have three building materials: wood, stone, and metal in ascending order of durability. You can farm all of them around the map, but ensure you aim for the flashing circles when harvesting with your pickaxe to speed up the process.