To be safe, use the actual Chicago Apartment Lease which is what is legally required in the city.
Google "Chicago lease" and it's the second link that comes up. It's free.
A few things you'll want to do:
Make two copies (sounds logical but many people forget)
If utilities are included or are to be split, make sure to write that in and initial it.
Anything that is 'out of the ordinary' make sure you write in, i.e. No pets except for Boas, or no hanging of presidential campaign material in the kitchen.
Even though the lease will have an end date, have a serious discussion about the importance of appropriate notice if your new roommate wants to move out so that they can understand it can't be done on a whim.
Collect a security deposit. I own a multi-unit in Chicago and I had one tenant get a roommate. He did a separate lease with this roomie, and held onto a deposit. That roommate left with short notice, and damaged his carpeting. He was able to use the security deposit to cover these things (the exact rules for security deposit use are spelled out in the Chicago lease.
Good luck. And don't fight over the remote.