Just a thought... Did you buy this building or renting? If you bought it Hows the roof? Reason I'm asking is if the roof is questionable you may be better off to insulate the roof (outside on top) then put on new roof. Then you can do away with the insulation that is now and will for ever be falling down. Just a thought. I wish my shop was that large, I'm sure I could get in to a lot of trouble then. ENJOY