Spray foam roof for large industrial building

[Michelle R.]

We have a 90000+ square foot flat roof industrial building. The roof itself is not in great shape. There are walls between the sections of the roof which are probable causes of some leaks. 

We are considering to put on a spray foam flat roof covered with a silicone coating. There is a 15 year manufacturer warranty. In theory, in 15 years when the silicone coating is starting to wear down, another such coating can be put on top economically.

We are curious to hear if anyone has put such a roof on their building and what is your experience with it. 

The flat roof is already a second layer so it would be pricy to tear down the old roofing material to start again with a new first layer. The price of the spray foam roof and coating is approx $3.50/ft.