user: Question: What is the arena capacity of the arena in the town whose head coach is Roberto Serniotti?
Columns: ['Previous season 2007/2008', 'Team', 'Town', 'Arena (capacity)', 'Website', 'Head Coach', 'Foreign Players (max. 2)']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['1', 'Dynamo', 'Moscow', 'Dynamo Sports Palace (5 000)', 'www.vcdynamo.ru', 'Daniele Bagnoli', 'Dante Amaral Alexis Gonzalez']
SQL:

assistant: SELECT "Arena (capacity)" FROM "Table" WHERE "Head Coach" = 'Roberto Serniotti';