WHY HVAC twice as much air?? extra windows?? why??? Hell, here in Florida we shade windoze as much as possible....
12-12 roofs are not walkable, 4-12 is all ANY house needs, even winters up north.....use metal roofs, standing seam, they don't make shingles NEAR as good as decades ago.....they don't even offer slate roofs either....ceramic seems to be a Ca./SW thing......
8-10' ceilings are fine.....and if you have a second story you really want very restricted airflow between them......
