Using Builder to also build encapsulated object

Imagine I have a class that encapsulates another class:

@Builder
public class Dragon {

  private Dimensions dimensions;
  private String name;

  public static class ParentBuilder {
    DimensionsBuilder innerBuilder = Dimensions.builder();

    public DragonBuilder height(double height) {
      this.innerBuilder.height(height);
      return this;
    }

    public DragonBuilder length(double length) {
      this.innerBuilder.length(length);
      return this;
    }

    public Dragon build() {
      return Dragon.builder()
        .dimensions(this.innerBuilder.build())
        .name(this.name)
        .build();
    }
  } 
}

@Builder
public class Dimensions {
  private double height;
  private double length;
}

Keep in mind that this is a very simplified example, the real code (which is, unfortunately, not about dragons) delegates a lot of properties to the innerBuilder.

This way, I can instantiate the class like this:

Dragon dragon = Dragon.builder()
  .height(12.0)
  .length(25.0)
  .name("Smaug")
  .build();

Instead of like this:

Dragon dragon = Dragon.builder()
  .dimensions(Dimensions.builder()
    .height(12.0)
    .length(25.0)
    .build())
  .name("Smaug")
  .build;

Is it good coding practice to add builder methods to directly build the inner class too? Or does it offend some design principle, because maybe it's too tightly coupled?

One issue I already encountered was when doing a refactor of the inner class, I also had to apply mostly the same refactorings to the parent class.