Comic book / colector card type shops usually sell all types of plastic sleeves, cases, etc for preserving paper items like a build sheet. They also sell really nice cardboard magazine boxes for storing old car magazines.

I would also make a color copy for reference, and put the original back in the car so the car and original build sheet don't become seperated. It seems when I buy a car the owner has the buildsheet, but cant recall where he stored it...