The overall dimensions are 1000mm wide x 1200mm long and 1000mm to the eaves and 850mm to the ridge. From then on the design can be sorted out from Pinterest.
A chicken is about 300mm high so we need to accommodate that in the perch and in the nesting box.
Step one is to get some materials.
The door aperture was too large and so I got a piece of ply to cover the hole and a doorway cut into that. The advantage is that the door is a feature and can be highlighted a special shape and painted with a different colour scheme.
Then I put a coat of paint on the roof to protect it and a pretty yellow door and its ready for delivery.