A clear plastic roof may be just what you need. You can get clear corrugated roofing at your local building supply store or try something a little different. The material in this photo is 1/2 inch thick honey comb plastic from Tap Plastic. I think it looks a little more upscale and diffuses the light nicely.
Grinch ornaments (I've made 10 of these): I decorated clear platic ornaments (with kids in mind) inside with Pledge floor wax and Martha Stewart glitter. Then I hot glued a snippet of green feather boa around the top. I punched yellow eyeballs with black centers out of duck tape sheets, and then cut out (free hand) eyebrows. Pretty simple... love the results.