学用状态机模式，写的报销流程，请指教

刚学编程不久，请前辈们指点。
需求变化点：不同的金额，和不同的角色走不同的报销流程

using System;

static class Factory
{
    public static Employee CreateEmployee(string name)
    {
        Employee employee = null;
        switch (name)
        {
            case "Sales":
                employee = new Sales();
                break;
            case "ProjectManager":
                employee = new ProjectManager();
                break;
        }
        if (employee == null) throw new Exception("传入的名字非法！");
        return employee;
    }
}

abstract class Employee
{
    public int Money { get; set; }
    public State State { get; set; }

    public void Sign()
    {
        State.ChangeState(this);
    }
}

class Sales : Employee
{
    public Sales()
    {
        State = new ProjectManagerState();
    }
}

class ProjectManager : Employee
{
    public ProjectManager()
    {
        State = new DepartmentManagerState();
    }
}

abstract class State
{
    public abstract void ChangeState(Employee employee);

    public virtual void ChangeState(Employee employee, string sign, State state)
    {
        Console.WriteLine(sign);
        employee.State = state;
        employee.Sign();
    }

    public virtual void FinishState(Employee employee, string sign)
    {
        Console.WriteLine(sign);
        employee.State = new FinishedState();
        employee.Sign();
    }
}

class ProjectManagerState : State
{
    public override void ChangeState(Employee employee)
    {
        if (employee.Money < 200)
        {
            string sign = string.Format("{0}元，项目经理签字报销", employee.Money);
            FinishState(employee, sign);
        }
        else
        {
            string sign = string.Format("{0}元，项目经理签字后，给部门经理", employee.Money);
            ChangeState(employee, sign, new DepartmentManagerState());
        }
    }
}

class DepartmentManagerState : State
{
    public override void ChangeState(Employee employee)
    {
        if (employee.Money < 1000)
        {
            string sign = string.Format("{0}元，部门经理签字报销", employee.Money);
            FinishState(employee, sign);
        }
        else
        {
            string sign = string.Format("{0}元，部门经理签字后，给总经理", employee.Money);
            ChangeState(employee, sign, new GeneralManagerState());
        }
    }
}

class GeneralManagerState : State
{
    public override void ChangeState(Employee employee)
    {
        string sign = string.Format("{0}元，总经理签字报销", employee.Money);
        FinishState(employee, sign);
    }
}

class FinishedState : State
{
    public override void ChangeState(Employee employee)
    {
        Console.WriteLine("签字完成，找财务报销{0}元", employee.Money);
    }
}

class Test
{
    static void Main()
    {
        Employee employee = Factory.CreateEmployee("Sales");
        employee.Money = 1150;
        employee.Sign();

        employee = Factory.CreateEmployee("ProjectManager");
        employee.Money = 2150;
        employee.Sign();
    }
}