When you have the opposing factions flag go to the roof, it is the best defensive position. There is only one way for the opposing faction to get in. Also, there are many ways to escape. This is basic knowledge however, some people may not know it. Now for the good stuff:
If you are on the roof, your healer is dead and you are also about to die, jump off the roof. Right when you jump, logout. Doing so will cause you to be suspended in the air for 19 seconds until your logout timer runs out. Make sure that you cancel the logout before the timer runs out. If you don't you will get logged out, crash to the ground, die and lose the flag. Loser.
These 19 seconds could help you a lot. They could give your team time to come to your rescue. Also, melee characters cant't hit you.