You would do something like this:
CREATE TRIGGER ddl_trig_database
ON ALL SERVER
FOR DROP_DATABASE
AS
PRINT 'Database Dropped.'
SELECT SYSTEM_USER, EVENTDATA().value('(/EVENT_INSTANCE/TSQLCommand/CommandText)[1]','nvarchar(max)')
GO
But you could even
INSERT INTO dbo.tblAudit (username, eventdata)
SELECT SYSTEM_USER, EVENTDATA().value('(/EVENT_INSTANCE/TSQLCommand/CommandText)[1]','nvarchar(max)')
You would need to create the table in the master or in a database that could be inserted into from that context, but you could keep an eye with this type of DDL trigger.