We would not recommend it. Adding more layers can hide any damage to your existing roof, including mold, rot, and water spots. It can also raise temperatures in your attic.
Will a metal roof make my house hotter? The answer to that question depends on two main factors.
Can you install a metal roof over shingles? Why is a metal roof more expensive than shingles?
Should I get a new roof before selling my home? Do I need to remove my old roof before installing a new one?
Consistent exposure to salty air can absolutely cause corrosion and rust over time if the metal roof is not properly treated and maintained.
While some may point out potential concerns with metal roofs, the benefits absolutely outweigh the drawbacks for Florida homeowners.
Depending on the circumstances and the materials, either option could cost a lot of money. What you want to focus on is longevity.
Gutters are often neglected, especially on two story homes. But with the Florida rain and wind comes debris and possible damage.