I want to build and add an external nesting box to my 3x5' coop - and I get the idea: build a 14x14x12" box with a hinged top and one side open, cut a smaller hole in the plywood wall of my coop (below the roost) and attatch the box to the side of the coop. How do I attach it though? There aren't studs to attach it to. I want to be sure its secure from predators and won't fall off and won't let water in, and I've not built anything real before. I have a drill and I will figure out what sizes my wood needs to be and ask a friend to pre-cut them for me. Are there instructions anywhere online where I can find a way to build a single external nesting box?