Since Google+ hasn’t offered RSS feeds for its streams, and PlusFeed was shut down because of the GAE price’s rising, I had no alternative way to create an RSS feed for a Google+ user's stream when which was asked for by Lorelle last year.
But luckily, there are alternative ways this year, and among which, the following 3 are the best for you to create an RSS feed for any Google+ user's stream, easily and free of charge:
1. Google+ to RSS

On the Google+ to RSS website, you need to enter a Google+ user's ID, your Google+ API key and your email address, then you can get the RSS feed URL (such as this).
By the way, to get your Google+ API key, you need to enable "Google+ API" on the Google API console first.
2. Google+ To RSS As A Service

With Google+ To RSS As A Service, you can enter your Google+ profile ID and click the "Go!" button to get the RSS feed URL, such as the following:
http://gplus-to-rss.appspot.com/rss/114785135385262933560
In fact, you can also replace "114785135385262933560" with any Google+ profile ID and add the above URL to your RSS reader directly.
3. Zipl.us

On the homepage of Zipl.us, you can pick a nickname, enter your Google+ ID, click on the "GO!", and enter the following URL into your browser address bar:
http://zipl.us/YourName/feed
Just replace "YourName" with your nickname, then you can get your RSS feed URL (such as this).
Bonus

Besides the above 3 websites, googleplusrss.nodester.com was also available for you to create an RSS feed for any Google+ user's stream by just adding their IDs behind its domain, as what you can see from the above screenshot, but it was down when this post was published.
Related free web apps: