Pattern for creating objects and set their common base and specific derived class properties

Question

I have a scenario to design a class structure to creates different types of derived class objects and set some of their common base class properties. Here is the final pattern I came up with to solve the problem. Can someone please take a look and advise if this a good design or can it be improved?

The domain model's ContractEmployee and FullTimeEmployee inherits from the base class Employee. The two properties of the base class DailyWorkHours and WeeklyHolidays will always have the same values for every Employee sub type.

The employee objects needs to be created using their respective Builder classes such as a ContractEmployeeBuilder or FullTimeEmployeeBuilder. These builder classes are exposed to the client using interfaces.

The Builder classes are responsible for creating the respective employee objects, set their properties as well as their base class properties. However I do not want every concrete builder class to to have the repeated code of creating the objects and setting the base class properties. So I have created a base class named EmployeeBuilderBase to achieve this.

The abstract EmployeeBuilderBase class can create the object, set common base class properties and calls an abstract method named SetProperties. The builder classes can override this method to perform any additional operations they want to do on the object.

/***Code Below*****/
using System;
using Microsoft.VisualStudio.TestTools.UnitTesting;

namespace EmployeeApp.Tests
{
    [TestClass]
    public class EmployeeBuilderTests
    {
        [TestMethod]
        public void CreateContractEmployee_ReturnsAContractEmployeeObject()
        {
            IContractEmployeeBuilder contractemployeeBuilder = new ContractEmployeeBuilder();
            ContractEmployee emp = contractemployeeBuilder.CreateContractEmployee(12, "ABC ltd.");
            Assert.AreEqual(emp.ContractDurationInMonths, 12);
            Assert.AreEqual(emp.DailyWorkHours, 8);
        }

        [TestMethod]
        public void CreateFullTimeEmployee_ReturnsAFullTimeEmployeeObject()
        {
            IFullTimeEmployeeBuilder fulltimeEmployeeBuilder = new FullTimeEmployeeBuilder();
            FullTimeEmployee emp = fulltimeEmployeeBuilder.CreateFullTimeEmployee("John Smith", 2500);
            Assert.AreEqual(emp.MonthlySalary, 2500);
            Assert.AreEqual(emp.DailyWorkHours, 8);
        }
    }

    ///*************************Domain Models*********************************************    
    public class Employee
    {
        public int DailyWorkHours { get; set; }
        public int WeeklyHolidays { get; set; }
    }

    public class ContractEmployee : Employee
    {
        public int ContractDurationInMonths { get; set; }
        public string AgencyName { get; set; }
    }

    public class FullTimeEmployee : Employee
    {
        public int MonthlySalary { get; set; }
        public string EmployeeName { get; set; }
    }

    ///*************************Interfaces and Abstract base class for the Builder Classes*********************************************    
    public interface IContractEmployeeBuilder
    {
        ContractEmployee CreateContractEmployee(int contractDurationInMonths, string agencyName);
    }

    public interface IFullTimeEmployeeBuilder
    {
        FullTimeEmployee CreateFullTimeEmployee(string employeeName, int monthlySalary);
    }

    public abstract class EmployeeBuilderBase<T> where T : Employee, new()
    {
        public T BuildEmployee(object options)
        {
            T obj = new T();
            obj.DailyWorkHours = 8;
            obj.WeeklyHolidays = 2;
            SetProperties(obj, options);
            return obj;
        }

        public abstract void SetProperties(T obj, object options);
    }

    //********Concrete Builder Classes***********************************
    public class ContractEmployeeBuilder : EmployeeBuilderBase<ContractEmployee>, IContractEmployeeBuilder
    {
        public ContractEmployee CreateContractEmployee(int contractDurationInMonths, string agencyName)
        {
            ContractEmployee contractor =
                BuildEmployee(new {ContractDurationInMonths = contractDurationInMonths, AgencyName = agencyName});
            return contractor;
        }

        public override void SetProperties(ContractEmployee obj, object options)
        {
            obj.ContractDurationInMonths = options.GetPropertyValue<int>("ContractDurationInMonths");
            obj.AgencyName = options.GetPropertyValue<string>("AgencyName");
        }
    }

    public class FullTimeEmployeeBuilder : EmployeeBuilderBase<FullTimeEmployee>, IFullTimeEmployeeBuilder
    {
        public FullTimeEmployee CreateFullTimeEmployee(string employeeName, int monthlySalary)
        {
            FullTimeEmployee emp = BuildEmployee(new {EmployeeName = employeeName, MonthlySalary = monthlySalary});
            return emp;
        }

        public override void SetProperties(FullTimeEmployee obj, object options)
        {
            obj.MonthlySalary = options.GetPropertyValue<int>("MonthlySalary");
            obj.EmployeeName = options.GetPropertyValue<string>("EmployeeName");
        }
    }

    //**** Object Extension method******
    public static class ObjectExtensions
    {
        public static T GetPropertyValue<T>(this object obj, string propName)
        {
            object value = obj.GetType().GetProperty(propName).GetValue(obj, null);
            return (T) value;
        }
    }
}

Answer 1

ContractDuration has no point of reference. Example: "6 months" from when? My suggestion would be to include a DateTime for the contract effective date, and then perhaps change the ContractDuration to be a TimeSpan.