This idea originated in the Philippines as a way of using empty PET Coke bottles in a corrugated galvanised steel roof.
I put two bottles about 90mm diameter in neat holes in the workshop roof, one with water in, the other with only air. They were placed vertically, half out, half in, sealed with clear silicon and each catch the sunlight and reflect it internally and downwards to the interior. There appears to be little, if any, difference in the brightness between the two, giving illumination roughly equal to about 60W each – enough to make it easier to find things on the shelves below without needing to switch on the usual fluorescent tube.
Even on a cloudy day sufficient light is transmitted.
The idea is well worth developing with wider diameter bottles which may perhaps increase the amount of light captured.
If there is lining below the steel roofing it should not reduce the efficiency very much, providing there is sufficient bottle height projecting above the roof.