namespace Shop.Model
{
    class Buyer
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
        public string PhoneNumber { get; set; }
        public bool BlackList { get; set; }
    }
}

using System.Collections.Generic;
using Shop.Model;

namespace Shop
{
    class Shop
    {
        List<Buyer> Buyers = new List<Buyer>();
        List<CatalogItem> CatalogItems = new List<CatalogItem>();
    }
}



namespace Shop.Model
{
    class CatalogItem
    {
        public string Title { get; set; }
        public string Model { get; set; }
        public float Cost { get; set; }
        public int Count { get; set; }
    }
}