Write SQL query to solve given problem: What percentage do items under the category of 'Furniture' make up the total number of items ordered that are shipped as standard in the West region?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT CAST(SUM(CASE  WHEN T2.Category = 'Furniture' THEN 1 ELSE 0 END) AS REAL) * 100 / SUM(T1.Quantity) FROM west_superstore AS T1 INNER JOIN product AS T2 ON T1.`Product ID` = T2.`Product ID` WHERE T2.Region = 'West' AND T1.`Ship Mode` = 'Standard Class'