This is a basing idea.
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The HeadQuarter would act like a base, and is similar to classic. There are 4-5 rooms a squad must go in to take the flag. Each room would be assigned(by the leader) a few members of the defending squad, and the final guarded by the leader and one other member.
E.G:
Squad A is defending, Squad B is attacking.
A-Leader assigns:
A-1 and A-2 to room one
A-3, A-4 and A-9 to room two
A-5, A-6 and A-7 to room three.
A-8 with himself in the final room.
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If a defending squad member dies, they must wait until all of the attacking squad members die, or the rest of the defending squad members in the room die. The attacking squad members get 5 seconds to advance. If no one is assigned to a room, the attacking squad simply advances to the next room.
EG:
Squad B has 5 members online(active): B-1, B-2, B-3, B-4 and B-Leader.
All of them attack room one. A-1 and A-2 die. Squad B advances to room two, and A-1 and A-2 respawn in their room (they cannot go into a different room unless the leader assigns them to a different room, though they can leave the tower whenever they want)
In room two, A-9 is offline, so only A-3 and A-4 can guard the room. A-3 dies, but A-4 manages to defeat all of Squad B. A-3 respawns in room two and A-4 is healed. Squad B's members decide to wait for everyone to die before attacking again.
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In the final room, the leader and the other member wait. They revive as soon as they die. If the attacking squad manages to secure the headquarter (shoot a block or something 20 times). Then the attacking squad wins.
EG:
Squad B makes it to the final room after a lot of struggle. A-Leader is killed by B-1, and revives. Eventually, Squad B shoots the block 20 times and they win the headquarter.
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Note:
-Once an attacking squad member dies, they cannot enter again until there are only 3 attackers left inside the HQ.
-The (defence) leader can assign a member to a different room, but they must die and respawn in that room, or leave and reenter the HQ at anytime.
-Any player can leave the HQ at any time.
-If the (defence) leader is not online a member may take the leaders place in the final room.
Sorry if this is confusing x.x I'm no good at explaining things.  

a-1 b-4 leader alpha bravo charlie omega 42;36428::2..:$

X.X  

This was a bit confusing xD but different bases would be better than the bases now  

This is confusing x.x.Why can't we just have a base in the middle like Comquest except it's on a hill and the attacking squad must get the up the hill and take it.

Attackers
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Do the same thing you spawn in little caves in the mountain at the bottom like a mine shaft.Once you spawn you run out the cave and make you way up to the hill.A course there will be fences,rocks,etc to hide behind because the defenders will shoot at you.Once you kill them you make your way into the base kill everyone you can but when you die you spawn outside the base.While your teammates die you keep going into different rooms(about 2-3 level) And once you get to the top you keep killing non stop still there is no more of there members up there once this happen you get the base and hold it for 1 minute.

Defenders
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Now the defenders is plain and simple because I mostly posted the other stuff in Attackers part.Your leader will tell you to go and assign you a post.For say you could guard outside.Or guard the stairs.Now I know a lot of you will say where will the defenders spawn.Well they will spawn in the basement or room that in the lower section.First when you spawn you come out of there and make your way out of the next level and come out under the stairs.

Now from reading this I counted about 12 levels but this will sound like a really fun planet .  

Basing is ruined, no need for anything that may work.