Initially, the Outpost is a small stone tower with some wooden planks leading to the door, a wooden awning circling the top of the tower, and a satellite dish and flag on top. There are windows around the top portion of the tower and some sandbags around the front. The dish is connected to a small wire.
At level 2, the satellite dish and wire slightly increase in size. The wooden awning extends slightly.
At level 6, the Outpost's overhangs become blue with the top one becoming corrugated metal. More sandbags and some crates appear around the Outpost. The wooden planks become stone slabs.
At level 9, the walls of the tower are thickened, the door's overhang becomes metal, the corrugated overhang around the top is replaced with a plated overhang, and more sandbags and some antennae are added. The stone slabs are a little darker with a very slightly different arrangement.
A Resource Base that has not yet been taken over by a player typically has an extremely low level Outpost. This is to make sure new Resource Bases get put into the matchmaking pool. Once you take it, the Outpost levels up to the correct level to match the levels of the base's Defensive Buildings.
The Outpost is a 4x4 building unlike the Headquarters which is a 5x5 building.
The Level 23 Outpost is currently the only level whose hitpoints is not divisible by 9, probably due to the stats not designed by the same developers.
Input total Statue bonus to modify the statistics in the table below accordingly