Okay, this is a big map with two unsafe ways to reach the other side. One only being available to the opposing team until it goes both ways at the last minute. Lets just accept that, and look at what tools we could be using. I do not advocate an offensive strategy in Turf Wars for this map because I believe it wouldn't be consistent enough, but this is merely my own opinion of whats most effective:
1) The first thing that comes to mind is beacons. My god are beacons a god send. Walking is a pain - especially if your a gatling or charger player. There are plenty of nooks and crannies to place a beacon, and you will want one close to the floodgate areas when they go down to keep the pressure up when you push in the late game.
2) The second thing that comes to mind is suppressive fire. This will most likely be the game half your team wants to play. One person should cut off the narrow walkways because it hinders the progress of the enemy and keeps them from their respective floodgate drop which you can't access yourself until the game is nearly over (this can be done simply by covering the wall that leads to it). One player should prioritize covering the areas leading to the ramps that go to your side - it's better to stop them there because from my experience most players have a special saved for when they are exposed on the grates. That player should also aim for the top of the walls because chargers favor them to pick your team off.
3) The third thing is having a designated painter and sentinel. This map is big, and having your side filled before the flood gates are open is vital. Rollers do have a purpose, and on this map it really should only be supportive until the last minute of the game. I recommend the Kraken Roller because you have beacons that can be placed down to help your team move about and the Kraken is good for emergencies. If you can do it early enough it helps to lay it down in the floodgate the enemy can't reach so your team can get ready for the last minute push. The sentinel needs to watch the grates at all times and stay in cover. Staying alive can mean the difference between holding your side or getting an enemy beacon set up on your side.
4) Push the enemy side hard once the floodgates drop. This is where beacons on the roof of the floodgate are welcome. If your roller did a good job the enemy will have too much ink to cover on your side, and more to loose on theirs because they tried to be offensive against your wall.
This map is annoying without a defensive strategy and it is what has worked for me. Take it with a grain of salt, and give any counter examples, thoughts etc.