The Iron Lantern is basically a Green Lantern version of Iron Man, I would check over at the uperhero Costuming Forum to see if they can give you any good ideas.
If you are in need of inspiration I'd check here. I'd also give "Iron Batman" a search, they both have potential for good looking suits, it just depends on the balance(or focus) of the design. Personally, I'd try to make it an equal mix of the two chosen heroes, but that's entirely up to you