To be clear, the city and county own the Gateway Sports and Entertainment Complex, not the Dolans.
I also do not see any way to 'add a roof' to it, it would need to be a completely new ballpark.
That said, both Jacobs Field and Browns Stadium should have been designed with a roof(or retractable roof), especially Browns Stadium. We will never host a Super Bowl without one, and the money generated from just a single Super Bowl would have paid for the damn roof. As of this year, Super Bowls generate between $300 and $500 million for the host city.