Bi-planes (or other propellor runway-takeoff & landing planes) would prefer roads but could land on any relatively flat area of terrain. When on roads, they'd move much quicker, particularly faster takeoff. After landing, they'd taxi to the control tower or some other building (there are plenty of existing models that can be used) for refuelling. Imagine if the scav tanker truck came out to refuel them!! (just like a repair droid will move towards a damaged unit)
And yes, Emdek, CLIFFS! We will do stuff with cliffs hehe.
