What do we want from it exactly?
Building X, say a farmhouse, on the map. Probably use somebody’s “UNIVERSE MAEKOR” code to swap out features with unit-versions of them, allied to GAIA. Similar to flags, have the building change teams based on the # of units in a small radius around (or in it). Building unit is a transport - infantry can enter into it like being ordered into a transport. Once infantry are loaded, they are stuck to point A (B, C, D, depending on building capacity) on the building model and can fire out from the building. Probably also cloak infantry who are inside buildings and disallow icon
Unless someone has a more advanced implementation in mind?
Can the inf be ordered to enter a non-same-team transport? The transport can be ordered to pick up units of any team, but I doubt the reverse is true (so the building may need to be ‘captured’ first, flag-style).
Can transported units be killed without destroying the transport? Again, I have doubts (never seen it happen). Because if they can be killed, then we can replace flags with those buildings on some maps (assigning a ‘strategic point’ value to a garrisonable thing sounds quite logical to me).
Assigning units to firing posts A, B, C, etc. is going to cause fire arc problems. If there are not enough inf in a building to man all the points, chances are the enemy can come from the direction no one is shooting at. Maybe a better approach would be to give the building a generic rifle/smg/lmg weapons and increase fire rate on those based on the number of inf inside (so even 1 man can in theory provide 360 degree fire arc by running from one window to the other ).