Hi Mike
In my neighborhood, barn roof structure tends towards being undersized. The tapered rafters are usually deformed in the upper levels. Adding on ceiling treatment, insulation and new roofing would not meet local codes and would require heavier rafters and purlins.
Look out for water seeping through foundation and moisture migration from ground into living space. Examine grade around barn and water drainage on lot. A barn is normally well vented, your house will be much tighter, warmer and more sensitive to moisture related problems.
Take care, Roger.
