Believe or not the is not much difference in osb and siding VS. Steel.
Pro's are it looks nicer with your home and the osb plywood stiffens your building up so it is stronger. Shingled roof cost a little more than steel but you will have to weigh that one out on what you want.
The reason the older steel buildings leaked is with the wind over time flexing your building would cause the steel to oblong the holes around your nails and wala you have a leak.
The new buildings have rubber washers on your nails. You also have a choice of buying screws which are better in the long run. They also have the rubber washers, which equals no leaks.
If you go with a steel roof, your steel is obviously corrigated. Make sure on the roof that you put your screws on the high ridges not the valleys. Sounds backwards and people are concerned about caving the steel in. You need to use a little common sense and stop when the screw is home. Anyways the andvantage to this is when it rains the water is going to run in the valleys so you have much greater odds of no leaks with your screws up on the ridges.
Hope this helps