It turns out that simple white paint gives almost as much benefit as a high tech reflector. If you paint the inside of your cover a stark white, you will get almost as much benefit as having the best high tech reflector. Any cover that must hold a light fixture needs to meet some basic requirements. It must allow the fixture to work without excessive heat build up, it must provide an efficient use of the light produced by the light tubes, it must continue to work after the first few months (which means it must not get the fixture wet). As far as plans, I know that some kit manufacturers, like AHSupply, do provide basic plans for a person to follow. What I do not find is that the plans offered are meeting any industry standards. I feel that the particular plans from AHSupply are decent enough that I would follow them with few reservations. That does not mean that they meet any particular national building standards, but merely that I find their plans adequate for me to use personally.