public class GenericRepository<T> : IGenericRepository<T> where T : class
{
    public virtual T Add(T entity)
    {
        using (ApplicationDbContext _db = new ApplicationDbContext())
        {
            DbSet<T> _table = _db.Set<T>();
            using (var transaction = _db.Database.BeginTransaction())
            {
                try
                {
                    var result = _table.Add(entity);
                    transaction.Commit();
                    return result;
                }
                catch
                {
                    transaction.Rollback();
                    return null;
                }
            }
        }
    }

    // and so on for other CRUD methods...
}

public class BuildingRespository : GenericRepository<Building>
{
    public Building GetFullBuildingById(long Id)
    {
        using (ApplicationDbContext _db = new ApplicationDbContext())
        {
            return _db.Buildings.Include(x => x.BuildingClient).FirstOrDefault(x => x.Id == Id);
        }
    }
    // ...and so on for other entity class-specific requirements
}