Our guys have maybe 3" boards to roost on - the just kind of hunker down on top of them and that's that. There haven't been any problems with them not being able to stay on, or losing their balance or whatnot. We did this because winters can get pretty cold here and we wanted to be sure their little toes wouldn't get frostbitten.
Despite our best efforts, there was a really nasty coldsnap and our flock is in their first year and didn't know any better to come in out of the cold. I was stupid and trusted their judgement. Two roos had really bad frostbite (one is still healing, the other looks horrible but seems fine so he's still with the flock). Minor frostbite is nothing at all to worry about - they bounce back super quick. What I observed was that everything looked fine the day-of, but by the next morning it was clear that all was not well. Their combs and wattles had mottled purply-black bits and some parts that were white. As the days went on, more of the white parts turned purply-deep-bruised-looking, and previously dark bits turned black. The affected skin has a rough, dry texture. If it gets severe, it can cause disorientation, lethargy, lack of appetitie, and other things - their bodies are in shock. I slathered vaseline and polysporin on them, massaging the parts that were still red to promote circulation, but just dabbing it on the damaged parts so as not to hurt them further.
Light frostbite usually only touches the tips of the comb, and it's normal for the little bit at the end to turn dark black and eventually fall off. Generally, even if it covers a larger area, you really just want to keep an eye on them to make sure the damaged skin isn't tempting to other birds. Watching for infection (you can smell it as well as see signs of it) is a good idea, too.
I quaranteened my rooster because he was having trouble eating (very swollen wattles) and also got his butt kicked by another rooster who took advantage of his frostbitten state. The healing process is veeeeeeeeeeeeeeeeery slow. They bounce back from light frostbite quickly, and even back to a functional state quickly, but full recovery from serious frostbite... I'm expecting not to see it until spring.
Thankfully, I've not had to deal with frostbitten feet, but from what I've read you want to bring those birds in as soon as you notice, because the chance of infection is quite high since it's their feet that have been injured.