Hi. My chickens are three months old now and I have been told that it is time to build nest boxes. So, of course I came here, looked at pictures posted, read the info, etc.. I noticed that most nesting boxes are actually a type of box ( sides and roof/top). Do they have to have tops? There is a long shelf in the coop right now with no sides or top. Is that okay? I was going to put small dividers on the shelf so each hen will have her own spot but without a roof. And is hay/straw the right choice for nesting material or should it be pine shavings? I use pine shavings on the floor of the coop. Thank goodness for this forum. I would be lost without it.