To the person saying use mortars, that's not going to work, as mortars do not do remotely enough damage, and are not accurate enough to reliably hit where you're aiming, as accuracy only increases when striking the same spot multiple times, so the roof campers just move to another edge of the roof and they're safe. Even if you spend 5 minutes and manage to mortar kill one of them, they just spawn on the beacon up there and go back to cheesing the map. Also, if you're spending the match mortaring, you're not capping or draining the enemy tickets, while the roof campers are draining tickets, even if they aren't capping anything up there.
The the person saying to adapt, the cap zones are designed with sightlines and cover in mind, the roof glitches are not accounted for. If they were getting under the map and shooting you from there, would you also say we should adapt? Nah, it's the same thing.
I think Apex has a good solution which is having the top surface of an asset starting an out of bounds countdown, that way you don't have an air wall that impedes you if you parachute from a chopper to back cap, etc..