Builder pattern

builder.cs

public class A {
    public A() {
        
    }
}

public class B : A {
    public B(string param1){
        
    }
}

public class C : B {
    public C(string param1, string param2){
        
    }
}

public static class Builder
{
    public static A Create<T>(){
        if(T is A){
            return new BuilderA();
        }
        if(T is B){
            return new BuilderB();
        }
        if(T is C){
            return new BuilderC();
        }
        
    }
    
    public class BuilderA{
        public virtual A Build(){
            return new A();
        }
        
    }
    
    public class BuilderB{
        protected string param1;
        public BuilderB setParam1(string param1){
            this.param1 = param1;
            return this;
        }
        public A Build(){
            return new B(this);
            //or return new B(param1); 
        }       
    }
    
    public class BuilderC{
         protected string param1;
         protected string param2;
        public BuilderC setParam1(string param1){
            this.param1 = param1;
            return this;
        }
        public BuilderC setParam2(string param2){
            this.param2 = param2;
            return this;
        }
        public A Build(){
            return new C(param1, param2);
        }
    }
}