Sounds to me like you have room for 4 birds. No, adding the roost does not figure in the space issue, sorry. I would not add any more since they will be in alot during the winter. I would say the double wall would be enough insulation since the birds produce a good bit of heat themselves. Things...
I remember someone has a coop that's individual walls held together with bolts (they knew they'd be moving) that could easily be taken apart. This would allow for the removal of one wall, a couple more added, the end put back on and the coop size is quickly doubled. This would allow for very...