Is there a way to create a monthly report of all of the RTC Project Areas that have been created since the last report was run?

I'll give you a suggestion. There are probably a lot of ways to do this.

For example, you could use the Java API and write a simple program that iterates over all the project areas in your repository and checks whether the creation date of each one falls between now and one month earlier. If it does, you list it up (or whatever you wish to do with it). Or you could pass the main method a month that you wish to check for newly created project areas etc.

Here is a useful snippet with IProcessItemService.findAllProjectAreas()
https://jazz.net/forum/questions/94479/how-to-get-the-active-project-areas-by-java-api

I would use the below resources to get a simple running example.
https://rsjazz.wordpress.com/2013/03/20/understanding-and-using-the-rtc-java-client-api/
https://jazz.net/library/article/1229