Using string to refer to variable

Since C# is object oriented, you might aswel make use of that.

You could create a template for your resources, unity has a nice way of creating and visualising data using ScriptableObjects

 [CreateAssetMenu(fileName = "Resource", menuName = "Resource")]
 public class ResourceConfig : ScriptableObject
 {
     public string Name;
     public int Limit;
 }

Create new resource template objects in your folder for each wood, gold etc..

Then assign them somewhere in inspector to your class

 // Our actual resource class we will use
 public class Resource
 {
     public string Name;
     public int Limit;
     public int Amount;
 }

 // Base class for all your production buildings
 public abstract class ProductionBuilding : MonoBehaviour
 {
     [SerializeField]
     private ResourceConfig[] _resources;

     public Resource[] CurrentResources { get; private set; }

     public virtual void Start()
     {
         InitializeResources();
     }

     private void InitializeResources()
     {
         CurrentResources = new Resource[_resources.Length];
         for (int i=0; i < _resources.Length; i++)
         {
             CurrentResources[i] = new Resource()
             {
                 Name = _resources[i].Name,
                 Limit = _resources[i].Limit,
                 Amount = 0,
             };
         }
     }
 }

 public class Woodcutter : ProductionBuilding
 {
     // In inspector u can assign wood here as resource for example
     public override void Start()
     {
         base.Start(); // Always call base if you wanna override start method
         Print(); // Log all selected resources
     }
     // Custom logic for this production building
     public void Print()
     {
         foreach (var resource in CurrentResources)
         {
             Debug.Log("Name: " + resource.Name + " | Amount: " + resource.Amount);
         }
     }
 }

So for example the woodcutter class you would assign to your gameobject in inspector and assign your resource templates. this will be your implementation of the ProductionBuilding class, that class is abstract that means it cannot be put in the inspector. (Intentional)

Each implementation will have CurrentResources which contains an instance of the selected resources.

https://www.youtube.com/watch?v=aPXvoWVabPY

You might try thinking about it more as general functions and a class for Resource. There's a lot of things you could do, but as a basic example to get from where you are now, you could try something like this:

 class Resource {
     string name;
     int amount;
     int limit;
 }

And your ResourceManager can have both general types instead of the specific values (you might use a List or Dictionary if there were a lot of resource types):

 class ResourceManager { // Don't know what you have here already
     Resource wood;
     Resource food;

     public Resource GetResource(string name) {
         if (name == "food") return food;
         if (name == "wood") return wood;
     }
     ...

Then, instead of your above two duplicate snippets, you'd call a function:

 AddResource(resourceManage.GetResource("food"));
 AddResource(resourceManage.GetResource("wood"));

 void AddResource(Resource resource) {
    if (resource.amount != ressource.limit)
      {
          AddGold();
          if (ressourceProduced + ressource.amount > ressource.limit)
          { .... you fill in the rest
     }