Builder.cs

class LineBuilder
{
    List<LineItem> _lines;

    public LineBuilder WithLine(params string[] names)
    {
        _lines.AddRange(names.Select(name => new LineItem(name)));
        return this;
    }

    public LineBuilder WithDepLine(object dependency, object target, params string[] names)
    {
        _lines.AddRange(names.Select(name => new DLineItem(dependency, target, name)));
        return this;
    }

    public IEnumerable<LineItem> Lines { get { return _lines; } }
}

CollectionMapTry2.cs

var result = obj.createResult(resultType, new LineBuilder()
  .WithLine("A")
  .WithLine("B")
  .WithDepLine(dependency, target, "C", "D", "E")
  .WithLine("F")
  .Lines);

return result;

// or this:


var result = obj.createResult(resultType, new LineBuilder()
  .WithLine("A", "B")
  .WithDepLine(dependency, target, "C", "D", "E")
  .WithLine("F")
  .Lines);

return result;