Honey, I'm an owner of the store located in Harrisburg, PA. We have a flat roof on our store and I guess I can replace your old metal ceilings?? We all HVAC equipment on the roof, what is the best way to put a new roof, my store is 2,100 square feet that need estimates of roofing contractors. From what I can tell … A metal roof is not a good idea. Ponding water will run through the seams are welded because even if the expansion and contraction of the seam will open. Ponding water will also make the steel roof rust prematurely. A better option is a rubber membrane roof. Guarantees, as long as 40 years are available. A reputable contractor roofing will make quick work of the task ceiling and be close to the problems that may develop. . In other words, they will be around to take care of warranty issues. Good luck with your roofing project.