This native app allows you to create a new calendar with the shifts (work days and days off)

You can also add holidays, local holiday, and observances with a brief description ( 19 countries: US, GB, CA, AU, DE, MX, RU, ES, FR, IE, IN, IT, NL, NO, PH, PL RO, TR, UA )

You can create a PDF file of your calendars or print using this app itself.

Also you can export your iPhone/iPad calendars.

If you're interested, please, look at the "basiCalendar" app much more generic.