interface IAggr
{
     int Volume { get; set; }
     double Price { get; set; }
}
interface IOrder : IAggr
{
     long Id { get; }
}

public class Build : INotifyPropertyChanged
{
     public event PropertyChangedEventHandler PropertyChanged;

     private IAggr _Aggr;
     private IEnumerable<IOrder> _Orders;

     public Build(IAggr Aggr, IEnumerable<IOrder> Orders)
     {
          _Aggr = Aggr;
          _Orders = Orders;
     }

     public int Volume { get { return _Aggr.Volume; } }
     public double Price { get { return _Aggr.Price; } }
     public int Count { get { return _Orders.Count(); } }
     public int Open { get { return _Orders.Sum(Item => Item.Volume); } }

     private void OnPropertyChanged(string Property)
     {
          if (PropertyChanged != null)
               PropertyChanged(this, new PropertyChangedEventArgs(Property));
     }
}

var Orders = new List<Order> { new Order(1, 11.0d, 1), new Order(2, 11.0d, 3), new Order(3, 12.0d, 1) };
var Aggrs = new List<Aggr> { new Aggr(10.0d, 1), new Aggr(11.0d, 5), new Aggr(12.0d, 3), new Aggr(13.0d, 4) };

BuildGridView.DataSource = new BindingList<Build>((from aggr in Aggrs join order in Orders on aggr.Price equals order.Price into orders select new Build(aggr, orders)).ToList());