There are plenty of lofts in the south and west loop areas of chicago, and you can get a pretty nice bang for your buck in these areas.
However, as Mansur stated, getting a loan with poor credit these days is very very difficult. That's not to say it can't be done; perhaps you both have great income, or you don't have poor credit, just little credit..... there are creative lenders/programs that you can utilize (note: I said 'creative', NOT predatory!).
Because there is so much inventory in the west and south lopps, it is also very possible that you will find a seller willing to do a lease purchase, but before entering into such an agreement, I would strongly advise that you have an experienced Realtor (one who understands lease purchases) write up the lease/contract and/or have an attorney review it prior to 'sealing the deal'.
It is also important you understand the difference between lease purchase and lease with and OPTION to purchase.
Finally, whether you end up getting a loan from the start and purchasing outright, or enter a lease purchase situation, since you plan on buying with a person not related to you by marriage or blood, it is important that you both sit down and work out how you plan to take title, what will happen if your relationship sours, what will happen if one of you decides to move for whatever reason.... These are all important things to talk about BEFORE getting into this type of financial commitment.
Good luck to you, and feel free to contact me with any questions (no, I'm not self-promoting, Trulians!)
You are asking if how this situation would work... and to be honest - it's destined to fail. BFF does not mean "forever" where money is concerned.
You will each have different priorities; with each one being more important than the other. As the mother of three grown children - I can tell you from experience that Murphy's Law will prevail.
Even the Best of the Best FF have bumpy areas.
If you decide to go forward; and you find a lending institution to actually grant the two of you a loan - make sure you have everything (& I mean everything with every possible scenario) planned and written out. Especially should one need to leave.
Otherwise, you could find yourself with worse credit scores than you started out with.