Include Error

//This compiles if all merged into one file, it also works with a makefile, unless I add #include "finance.h" and #include "freight.h" just below this line. Both of those classes that interact with nothing as of yet. Adding them to the includes and leaving part_time.h at the bottom breaks it, putting part_time.h at the top of the includes compiles.
//main.cpp

#include <iostream>
#include <string>
#include <stdlib.h>
#include <vector>
#include "casual.h"
#include "dockhand.h"
#include "employee.h"
#include "manager.h"
#include "part_time.h"
using namespace std;

void add_casual()
{
    string name;
    bool forklift;
    name = "bill";
    forklift = true;
    Casual casual(name, forklift);
}

void add_part_time()
{
    string name;
    bool forklift;
    int annual_leave;
    int sick_leave;
    name = "Ben";
    forklift = false;
    annual_leave = 1;
    sick_leave = 2;
    Part_time part_time(name, forklift, annual_leave, sick_leave);
}

void add_dockhand()
{
    int dock_type;
    dock_type = 1;
    if(dock_type == 1)
        {
            add_part_time();
        }
        else if(dock_type == 2)
        {
            add_casual();
        }
        else
        {
            cout << "Sorry. Your input is invalid." << endl;
            add_dockhand();
        }
}

void add_manager()
{
    string name;
    name = "Bub";
}

int main()
{
    cout << "Hello" << endl;
}

//casual.h
#ifndef CASUAL
#define CASUAL

#include <string>
#include "dockhand.h"
using namespace std;

class Casual: public Dockhand
{
    public:
        Casual (string set_name, bool set_forklift);
        float min_shift;
        ~Casual();
};

#endif // CASUAL

//casual.cpp
#include "casual.h"

Casual::Casual (string set_name, bool set_forklift) : Dockhand (set_name, set_forklift)
{
    min_shift = 2.00;
    payrate = 26.00;
}

Casual::~Casual()
{

}

//dockhand.h
#ifndef DOCKHAND
#define DOCKHAND
#include <string>
#include "employee.h"
using namespace std;

class Dockhand: public Employee
{
    public:
        Dockhand (string set_name, bool set_forklift);
        float start_shift;
        bool forklift;
        float payrate;
        ~Dockhand();
};

#endif // DOCKHAND

//dockhand.cpp
#include "dockhand.h"

Dockhand::Dockhand (string set_name, bool set_forklift) : Employee (set_name)
{
    forklift = set_forklift;
    start_shift = 4.00;
}

Dockhand::~Dockhand()
{

}

//employee.h
#ifndef EMPLOYEE
#define EMPLOYEE
#include <string>
using namespace std;

class Employee
{
    public:
        Employee (std::string name);
        string name;
        ~Employee();
};

#endif // EMPLOYEE

//employee.cpp
#include "employee.h"

Employee::Employee (string set_name)
{
    name = set_name;
}

Employee::~Employee()
{

}

//manager.h
#ifndef MANAGER
#define MANAGER
#include "employee.h"

class Manager: public Employee
{
    public:
        Manager (string set_name);
        float salary;
        ~Manager();
};

#endif // MANAGER

//manager.cpp
#include "manager.h"

Manager::Manager (string set_name) : Employee (name)
{
    salary = 52000.00;
}

Manager::~Manager()
{

}

//part_time.h
#ifndef PART_TIME
#define PART_TIME
#include <string>
#include "dockhand.h"
using namespace std;

class Part_time: public Dockhand
{
    public:
        Part_time (string set_name, bool set_forklift, int annual_leave, int sick_leave);
        float end_shift;
        int annual_leave;
        int sick_leave;
        ~Part_time();
};

#endif // PART_TIME

//part_time.cpp
#include "part_time.h"

Part_time::Part_time (string set_name, bool set_forklift, int annual_leave, int sick_leave) : Dockhand (set_name, set_forklift)
{
    end_shift = 8.00;
    payrate = 22.00;
}

Part_time::~Part_time()
{

}

//finance.h
#ifndef FINANCE
#define FINANCE
#include <vector>
#include "freight.h"
#include "employee.h"
using namespace std;

class Finance
{
    public:
        Finance();
        ~Finance();
};

#endif // FINANCE

//finance.cpp
#include "finance.h"
using namespace std;

Finance::Finance()
{

}

Finance::~Finance()
{

}

//freight.h
#ifndef PART_TIME
#define PART_TIME

#include <string>
using namespace std;

static const float MAX_SATCHEL_VOLUME = 0.20; // in m^3
static const float MAX_CARTON_VOLUME = 0.50; // in m^3

static const float SATCHEL_COST_PER_KILO = 2.00; // in dollars
static const float CARTON_COST_PER_KILO = 1.00; // in dollars
static const float PALLET_COST_PER_KILO = 0.50; // in dollars

class Freight
{
    public:
        enum FreightType
        {
            SATCHEL,
            CARTON,
            PALLET,
        };
        float cost()
        {
            return perKiloCost * weight;
        }
    private:
        Freight (string set_address, float set_length, float set_width, float set_height, float set_weight);
        string address;
        float length;
        float width;
        float height;
        float weight;
        FreightType type;
        float perKiloCost;
        ~Freight();
};

#endif // FREIGHT

//freight.cpp
#include "freight.h"

Freight::Freight (string set_address, float set_length, float set_width, float set_height, float set_weight)
{
    address = set_address;
    length = set_length;
    width = set_width;
    height = set_height;
    weight = set_weight;
    type;
    perKiloCost = 1.00;
        {
            float volume = length * width * height;
            if(volume > MAX_CARTON_VOLUME)
            {
                type = PALLET;
                perKiloCost = PALLET_COST_PER_KILO;
            }
            else if(volume > MAX_SATCHEL_VOLUME)
            {
                type = CARTON;
                perKiloCost = CARTON_COST_PER_KILO;
            }
            else
            {
                type = SATCHEL;
                perKiloCost = SATCHEL_COST_PER_KILO;
            }
        }
}

Freight::~Freight()
{

}