Builder Pattern in C#

The Builder Pattern helps you create complex objects step by step. It separates the construction of an object from its final structure, so you can use the same process to build different versions.

Real-Life Analogy: Building a House

Imagine you want to build a house. You don't go out and build the whole thing at once. There's a clear process: lay the foundation, build the walls, install the roof, add plumbing, and paint the interior.

A builder knows the steps. You just tell them what kind of house you want — small or big, with a garage or without — and they follow the steps to build it. The process stays the same, but the details can change.

Benefits of Builder Pattern

The Builder Pattern helps manage complex creation logic and makes your code cleaner. It also avoids using a long constructor with too many parameters.

Key benefits:

• Step-by-step object creation
• Flexible and customisable output
• Same process for different results

When Should You Use It?

The Builder Pattern is great when creating an object with many parts or options. Instead of passing everything to a constructor, you build the object step by step.

Use it when:

• An object has many optional parts or configurations
• Construction needs to be done in steps
• You want to reuse the building steps for different final outputs

When Not to Use It: Don't use Builder when the object is simple, doesn't have many parts, or can be built easily using a constructor or factory.

What to Implement

To use the Builder Pattern, you need to create:

• Product – the final object being built
• Builder interface – defines the steps to build each part
• Concrete builder – implements the steps for a specific result
• Director – manages the build process order

How It Works in C#

// Product
public class House
{
    public string Foundation;
    public string Walls;
    public string Roof;

    public void Show() =>
        Console.WriteLine($""Foundation: {Foundation}, Walls: {Walls}, Roof: {Roof}"");
}

// Builder Interface
public interface IHouseBuilder
{
    void BuildFoundation();
    void BuildWalls();
    void BuildRoof();
    House GetResult();
}

// Concrete Builder
public class WoodenHouseBuilder : IHouseBuilder
{
    private House house = new House();

    public void BuildFoundation() => house.Foundation = ""Wooden Piles"";
    public void BuildWalls() => house.Walls = ""Wooden Panels"";
    public void BuildRoof() => house.Roof = ""Wood Shingles"";

    public House GetResult() => house;
}

// Director
public class ConstructionDirector
{
    public void Construct(IHouseBuilder builder)
    {
        builder.BuildFoundation();
        builder.BuildWalls();
        builder.BuildRoof();
    }
}

Usage:

var builder = new WoodenHouseBuilder();
var director = new ConstructionDirector();

director.Construct(builder);
House house = builder.GetResult();
house.Show();

Final Thoughts

The Builder Pattern is like hiring someone to build your house. You explain what kind of house you want, and they follow the steps to create it — one part at a time.

It makes object creation easier, cleaner, and reusable — just like building a small cottage or a large villa using the same plan.