You could look around those websites that are looking for freelance coders and look at the projects they have. You can either just accept the job or use the job description as a problem statement and develop the "core" part of it. Here are a few examples on rent-acoder you could try out:
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My company needs a simple webapp thats does the following:
allows our ACTIVE DIRECTORY users to reset their passwords by entering their email only in the case they forget their username.
JAVA OR PHP prefered.
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Create a Windows executable file. Every time it runs it will download a csv file from a published Google Drive HTTP Link, and place the file on SFTP. It needs to run 3 times per day. Morning, afternoon, evening.
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Can you write a small program/website for me that prints out tweets in realtime?
By the looks of it, the listed prices are extreme lowballs for what some people are asking, but like I said, you can just take what they are asking and develop on your own as practice.