You can use 2x2's for roosts if you have bantams but I usually stick with 2x4's with the 4" side for them to sit on. In the winter they can sit so that all their fluff will cover the entire foot and protect it. And if you have the bigger birds like Jersey Giants then they have no trouble at all with 2x4's.
And I say go for as much ventilation as you can! Most everything I have is very open and we get a lot more snow and cold over here than you get. Birds get too much respiratory problems and die from heat stress with any less air flow. Block the wind and they are happy.
Sorry to cut into your thread, but on an 8 x 10 shed, how much ventilation do you suggest? There is some ventilation around the roof, but do we need some in the sides?