Take a normal 20 ounce coke bottle and wash it out. Fill the bottle with water and add one bottle cap full of bleach. Fill to the very top leaving no room for a air pocket and then cap it. Now you can remove the label.
Next, drill a three inch hole in your roof and install the coke bottle. Silicone all around it to keep the roof from leaking.
On the inside you will have to strap the bottle in place so it will not fall out. Silicone the underside of the roof and let sit for about six hours before removing the strap.
There you have it. A solar light that is equal to a 40 watt soft light bulb with now wires, solar equipment or the expense.
This light was installed into a solar bathhouse built at http://moderndayredneck.blogspot.com