As to roosts, the last set we built using 2x4s, but laid them flat so they roosted on the 4" side (technically 3 1/2"). After doing some research on here and talking with some of our friends, using the wider side helps in the winter so that the birds can cover their feet when they roost. Also with our large fowl birds they seem to be more stable with the wider roosts. the draw back is potential warping the center depending on the length of the roost and weight of birds. Our roosts are not that long so warping is not an issue.
I don't know if one way is better than the other and am not an expert by stretch of the imagination, but wanted to share. We have built roosts several different ways in our two coops, and I'm sure we will build them a different way the next time around.
I am forever amazed how the birds will choose the highest point they can to roost. Our 8 lb orp rooster prefers to perch about 8 ft up on a sliver of an overhang for the nesting boxes. Go figure how he gets up there and gets down...