Good morning all i have just enrolled in this new forum. i have a question regarding rafter sizes. we are constructing a new roof over existing lean too rear of the house, it is 5.5m x 3m x 3m external walls are in place with catnic lintels over window and doorway a 4" x 4" wooden header runs across the front span with a 6" x 2" wall plate fitted. i would like to know what size rafters should i use as the roof construction, roof will be corrugated metal and the weight reduced from using a concrete roofing tile.