You can create websites on many of your interests. I created lots of websites on health and fitness for example, because I’m interested in those topics. You can create websites on any topics in which lots of people are interested, and sell them.
Of course, you can also create websites according to the calendar. Christmas comes around every year. So if you created several websites now, they would be well-established, in time for you to get some extra income over the Christmas holiday period.