I am installing a wood burning stove. I had on old zero clearance fireplace, which I have ripped out. On the roof, the old chimney and roof flashing (from the zero clearance fireplace) is much too wide for the 8" od class A pipe. The only storm collar I can find is too small to cover that chimney. I hate to mess with my roof by putting in new flashing. I am thinking I can make my own storm collar, but am wondering if this is ok. Or, does someone sell storm collar that is wider than 5 1/2 inches... it needs to be more like 8" to reach the outside of the old chimney