Large Scale Central

Lighting

I have been planing on adding lighting to the structures on my railroad and I was just wondering what the best method of doing this would be. It would be nice to have a diagram or drawing if possible with a reply but is not necessary. The only problem I am coming across with is how do I protect my wiring from water damage?
I would also like my lights to look as realistic as possible because some of my buildings are open like my saw mill and you could easily see any lighting installed on the ceiling.