请教关于C# 三层架构的问题！！求指点！！

MODELS层：ROOM.CS: 
public class Room
    {
        //public Room() { }        private int roomId;
        private string number = String.Empty;
        private int bedNumber;
        private string description = String.Empty;
        private string state = String.Empty;
        private int guestNumber;
        private RoomType roomType;        public RoomType RoomType
        {
            get { return roomType; }
            set { roomType = value; }
        }        public int GuestNumber
        {
            get { return guestNumber; }
            set { guestNumber = value; }
        }        public string State
        {
            get { return state; }
            set { state = value; }
        }        public string Description
        {
            get { return description; }
            set { description = value; }
        }        public int BedNumber
        {
            get { return bedNumber; }
            set { bedNumber = value; }
        }        public string Number
        {
            get { return number; }
            set { number = value; }
        }        public int RoomId
        {
            get { return roomId; }
            set { roomId = value; }
        }
----------------------------------------------------------------------
DAL层：RoomService.CS：
public int AddRoom(Room room)
        {
            string sql = "insert into Room(Number,BedNumber,Description,State,GuestNumber,TypeId)" +
                " values(@Number,@BedNumber,@Description,@State,@GuestNumber,@TypeId)";
            sql += " ; select @@identity";
            SqlParameter[] para = new SqlParameter[]
            {
                new SqlParameter("@Number",room.Number),
                new SqlParameter("@BedNumber",room.BedNumber),
                new SqlParameter("@Description",room.Description),
                new SqlParameter("@State",room.State),
                new SqlParameter("@GuestNumber",room.GuestNumber),
                new SqlParameter("@TypeId",room.RoomType.TypeId)
            };
            return DBHelper.GetScalar(sql, para);
        }
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错误：
错误 1 “HotelModels.Room”不可访问，因为它受保护级别限制
错误 2 可访问性不一致: 参数类型“HotelModels.Room”比方法“HotelDAL.RoomService.AddRoom(HotelModels.Room)”的可访问性低
不知道咋回事》？？求各位大侠指点迷津！！