Just purchased a used greenhouse - need advice

[catalekid]

I just purchased a used greenhouse that is no longer being utilized by our local supermarket. It is 21' X 30' and has everything, shelves included, except the roof covering. I plan to use this greenhouse to extend my growing season.

My question is this: Do I want clear or white plastic sheathing? Anybody have a good lead on where to purchase it that provides good service and a good price?

I only need enough for the top as the sides are sliding polycarbonate.

Thanks if you can help.