Some roost designs may prove better when birds tend to crowd pushing somebody off. The round, more natural shape limits the angles birds can push each other from although even 1 x 2 lats can provide that benefit and are much cheaper than dowels produced by expensive milling. Frostbite risk in my experience at higher latitudes and little or no protection from winter conditions has little to do with roosting arrangements other than the birds need to be up on dry surfaces that are good insulators of heat which wood is a good example.