As the humans, can you build in a region you have taken control of, using airfield, even if it has a Trog token? So...no human minis in the region.
So long as you control a region you can build structures into it, regardless of any unresolved Trog or exploration tokens that are also present. A caveat, you must control the region at the start of a build/activate structures action, this prevents chaining control across the map.
Lastly if the region is controlled by you, but also a Battle Region, you may only build into it if the structure you are building explicitly says you may.