A lot of people like to use the largest side of a 2 x 4 (lay it flat) for them to roost on, as they can cover their toes with feathers when it is cold. This helps to prevent frostbite on the toes.
If you have heavy breeds it is good to have the roosts not too high. Higher than nest boxes is important if you can swing it. I have generally been of the opinion that roosts 3 feet up were a bit too high for my heavy brown egglayers in the past, but you have to accomodate your coop design as well. If they are too high they are at risk for bumblefoot. Everyone has different ideas- you will find your perfect design.
1/2 inches is just a bit too small IMO. I would go with the 2 x 4s.
I hope this helps- enjoy your chickens!