One thing I would highly recommend is to set your roost boards (even limbs) in a "u-shaped" hanger of sorts so that you can easily remove the roost to do a deep cleaning every so-many months. By screwing or nailing your roosts into the wall they are somewhat permanent...just FYI. :yiipchick
And if you get below freezing, set up the perches so that they perch on the four inch wide side.