There is a park and ride official one that is in Altstetten. You then get on the number 2 tram to Paradeplatz. Cost is by the hour with a limit of 15 francs. Then if you only want to park for up to 3 hours you can park in Letzipark where the first 3 hours are free it is also more or less on the tram number 2 line. From either you need around 15 minutes to Paradeplatz.