Here's the SQL query you can use:

```
SELECT CustomerID, SUM(OrderAmount) AS TotalOrderAmount
FROM orders
GROUP BY CustomerID
ORDER BY TotalOrderAmount DESC
LIMIT 5;
```

This query uses the `SUM` function to calculate the total order amount for each customer, then groups the results by customer ID. The `ORDER BY` clause sorts the results in descending order by the total order amount, and the `LIMIT` clause returns the top 5 rows.
Data una tabella di ordini cliente con colonne CustomerID, OrderID, OrderDate e OrderAmount, scrivi una query SQL per trovare i primi 5 clienti che hanno effettuato gli ordini più grandi.