I would make a dungeon that is like a whole bunch of dimensions fixed together. Like, it starts off as a regular temple (like the temple of time for example...) and you suddenly find this ominous door and you are in a field of snow, from there you head to a forest and it goes on like that. I just want it to be unique. As for the Item, it would be a special type of mayl that protects you from the elements. Kinda like the magic armor from
tp except it deosnt consume rupees, and it isnt so overpowered. It raises you defense against elemental based attaks, while you take standard damage from non-elemental attacks. The boss would be this huge demon like beast, that assaults you with a plethora of elemental based attacks (hence, the new mayl comes into play) and his attacks get fiercer and stronger as you kill him.
That would be the dungeon I'd like to create. I dont know how others will react to it, but I find it to be a unique and refreshing dungeon, as opposed to all the single element based dungeons in zelda (not that I have a problem with them).