I've heard tons of stories of why the bottles are placed on top of rebar on the roofs in Mexico. My builder just gave me the only answer that makes any sense to me. No it is not to keep them dry and it's not to bring attention that the house is unfinished. You guys get to make a guess or two ....
Rebar sticking out of the roof makes a great lightning rod .... and either glass or plastic will act as insulators
