im looking to create a big team battle in either the island or the valley area but i haven't a clue what i want to do and id like to see if anyone has any ideas for what i can doin either of those two areas.
You could try a map with a few vehicles, 2 bases at opposite ends with some balanced weapons and spawns, maybe throw in some cover and an aesthetic center piece.
I'm not sure what level of response you're really expecting considering how vague your prompt is. Island or Canyon? It depends on what kind of flow you want. The Island is essentially a giant circle with some infantry pathways cutting through the center. The Canyon will pit the teams head-to-head, unless you place a particularly interesting layout in there. Either works well. I think the Island might be an interesting place to set a 1-Flag/1-Bomb BTB map, with a sprawling base on one beach for the defenders and a smaller one for the attackers. If you want some inspiration or examples, I'm sure you can find a lot if you browse through Forge Hub's archives or Bungie.net user files. Good luck.