NOTICE:
I just updated this map. Here is the new download link:
http://halo.xbox.com/en-US/haloreach/none%20ya%20biznus/fileshare?#%21/?section=MapVariants&MapId=&GameMode=0&SearchDate=7&SortBy=2&view-select=Tile&tags=&startIndex=0&details=29762743http://halo.xbox.com/en-US/haloreach/none%20ya%20biznus/fileshare?#!/?section=MapVariants&MapId=&GameMode=0&SearchDate=7&SortBy=2&view-select=Tile&tags=&startIndex=0&details=29779091
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Silo is a small map, intended for 1v1 and functional with 2v2 Slayer, as well as FFA with 2-4 players. As such, This map is my submission for the 1v1 Smackdown contest.
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Now, on to the layout. Silo is a cyclic map, with 3 main floors surrounding a central area. Each floor goes around about 1/3 to 1/2 the outer edge, never overlapping an adjacent floor (2 doesn't cover 1, 3 doesn't cover 2, but 3 covers 1). Each floor is connected to the others by ramps in the out rim, and there is also a man cannon from floor 2 to 3, going through the center. The center has several platform to jump across, as well as a ramp from floor 1 to 2. This area houses several advantageous weapons, but being in the middle, it is hard to avoid enemy fire (classic risk vs. reward). As this is a smaller, more CQC-oriented map, there are no parts there just to act as cover.

And yes, you are supposed to be able to stand on the brace, large ring going around the outer walls.
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And that brings me to gameplay. As I said before, this is a small map. So, speed and agility are required to set up each gunfight. It takes less than 8 seconds to travel across the map, so one should always be ready for a gunfight. Obviously, gameplay is naturally fast. While playtesting, I found that the outcome of a gunfight depends mostly on how quickly you can gun down your opponent. Taking extra time to aim your shots is usually a fatal mistake.
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Next, there are the weapons and their positions. There is one of all the listed guns, and 2 of each grenade.

Spiker+frag grenade: 1st floor, red spawn side, by ramp to 2nd floor.
Assault rifle+frag grenade: 1st floor, underneath 3rd floor.
Needle rifle: 2nd floor, by man cannon.
DMR: 3rd floor, by landing pad.
Magnum+plasma grenade: center, jumpable platform.
Plasma pistol+plasma grenade: center, ramp.
Custom powerup: center, jumpable platform.

There are also 3 health packs, 2 are on the 1st floor, underneath the 3rd floor, and one is at the top of the ramp from red spawn to the 2nd floor.

Upon update, a plasma battery guards each health pack to prevent use in the middle of a gunfight.
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Finally, the pictures (Some may be slightly outdated, but the map is almost exactly the same):

Initial loadout camera (shows center magnum platform):

Red Spawn (1st floor):

Blue Spawn (2nd floor):

Man Cannon (2nd floor). Needle rifle spawns right behind it:

Landing platform for man cannon on the 3rd floor:

First floor, directly beneath 3rd floor:

Center custom powerup platform by ramp:

Center ramp and magnum platform:

Action Shots (I'm red btw):

3rd floor, by landing pad.

Center area, blue is using the man cannon, red is on the first floor.

Second floor, by the man cannon.

Center, jump from ramp to custom powerup platfrom.

Special thanks to Eriburrito (blue), who helped me test it.