How about this, go to home depot or what ever and buy some sheets of foam. the kind that they use on the outside of a buliding. You can cut, carve, sand(60 grit) what ever you want into it. After that coat it with a roof coating (cool seal) that will kind of incase it it rubber. Than paint it.

What you will end up with is this, a removable wall cover that you can stick (velcro) to the out side of the building that you can take down and store inside after halloween.

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