Once you have the map structure determined, you can move on to your unit data structures.
Mobile units are the warriors, tanks, aircraft, and so on, that actually move around the map.
The stationary units, on the other hand, are the buildings or building segments that do not move. The common elements of mobile and stationary units include an identifier, a map location, an owner, and so on. These common elements may allow you to use object-oriented techniques and create a common ancestor class for both kind of units, but that depends on the game and game logic needs. Stationary units generally do not move around the map. This can simplify how you handle stationary units.