[gregpark]

My rafters are 15" on center which provides a 12" bay. What are you going to do for a lid? I used corrugated tinted polycarbonate. The space is illuminated but not too hot at noon. Stronger than wood, never rots, fast and easy install. My slope drop is 3" in 12'. It looks like a flat roof but sheds water perfectly. That's ¼" drop per foot, the minimum to avoid ponding water. Nice well illuminated space