I am curious if anyone has experience making a free app and adding ads to it and placing it on the marketplace. Are ads difficult to code, and how do you actually go about doing that? How was the income with ads, do you think making a free app with ads is more profitable than selling it for $0.99 or really depends on the app itself? Thanks for the comments.
It is very easy to add ads to your app. See https://developers.google.com/mobile-ads-sdk/docs/ for the details. I've one app with Adds in the Play Store. It really depends on your app. When your App is used every day by the user you generate more views than an App that is used only once a month. You need a lot of downloads (100.000+) to get an income from it. With < 10.000 downloads you only earn a few dollars a week.