main.cc

#include "Point.h"

int main(int argc, char** argv)
{
  Point p;
}

main_builder.cc

#include "Point_build.h"

int main(int argc, char** argv)
{
  auto p = Point::build().set_x(0.0).set_y(0.0).set_z(0.0);
}

Point.h

#ifndef POINT_H_
#define POINT_H_

class Point
{
  public:
    class build;

    double x;
    double y;
    double z;
};

#endif

Point_build.h

#ifndef POINT_BUILD_H_
#define POINT_BUILD_H_

#include "Point.h"

#include <utility>

class Init_Point_Z
{
  public:
    explicit
    Init_Point_Z(const Point& msg) : msg_(msg) {}

    Point
    set_z(double val)
    {
      msg_.z = std::move(val);
      return std::move(msg_);
    }

  private:
    Point msg_;
};

class Init_Point_Y
{
  public:
    explicit
    Init_Point_Y(const Point& msg) : msg_(msg) {}

    Init_Point_Z
    set_y(double val)
    {
      msg_.y = std::move(val);
      return Init_Point_Z(msg_);
    }

  private:
    Point msg_;
};

class Point::build
{
  public:
    build(){}

    Init_Point_Y
    set_x(double val)
    {
      msg_.x = std::move(val);
      return Init_Point_Y(msg_);
    }

  private:
    Point msg_;
}; 

#endif