Something you buy, throw at the ground, and defend for 10 seconds. Once it's up, your landing site expands up to that beacon. If it's taken down, no more landing in that zone.

I don't really know the magic behind how landing site size is determined, but I'm willing to give making this a go myself if someone does know but doesn't want to make it themself.

Activity:SetLandingZone(Vector(x, y), player);

That is the relevant function, but I believe (untested) that only one LZ can be active per player, so you'll have some work on your hands if that's true. Might be able to (in theory) overwrite the LZ if the beacon is an actor and you set a new LZ when the beacon is selected. Though, like I said, I've not tested anything.