If you'd like to add some custom information to the confirmation email/receipt that ticket buyers receive upon completing their order you can add a Post Purchase Message and/or Event Restrictions to your event.
Restrictions would be used to convey an important event policy like your rainout policy, while a Post Purchase Message would be used to convey important instructions for attending the event, like parking guidelines.
To do this, first go to the Events tab and then click on the name of your event. Then from the Event Home, select the Details option.
Next, scroll down to the Restrictions and Post Purchase Message fields and click the edit option to edit one or both of them.
Whatever you enter in these fields will be displayed in the confirmation email below the option to download the tickets or view the receipt and will look similar to the example below.