What Can I use as a roof for my bird house?

I am making a Birdhouse for a contest. I a going to decorate it with recyclables. thats the contest "green Yard Ornaments/decorations" I have a metal base/box/ Bin. And it has a large enough hole for birds to get in, but it needs a roof. i have wood, but i would rather not use that, because i would have to cut it, and that would be difficult, for i can not use power tools without a parent and mine are working. I would like to use something that had another use, for example would like to use something "recyclable" like a milk jug. any ideas?