Hi Alianne! I think I can help you on the reference part:
The full body picture of Rose in Dragoon formThe same picture but hopefully a clearer oneAnd here's a close-upAs for how to make it, I'm afraid I can't help you much on that part since I haven't really tried building a costume personally because I'm still in the stage of being comfortable and happy with going with dress-type costumes. For the wings, though, the nearest material I can think of is green cellophane but this can really get destroyed easily because it's very fragile so you might want to look for an alternative on that one. I can't help you with the armor either so I think you better consult with the real builders around here like polidread and evaguy. I've provided you the images so they might answer here soon. ^^
Good luck on your costume plan! I'll be rooting for you kasi I also played the game myself and though it's a tiring game (the Additions especially) and the story's a bit of an old record, I enjoyed the graphics very much so I continued playing it until the end. My fave character's Meru, btw, kasi kulit niya eh, lol. :D