There are quite a few coops in Chicago, and most require that all adult occupants (excluding live-in help) are approved by the board prior to your purchase. Renting is often expressly prohibited except under extenuating circumstances, and only then with a complete application and board approval. Most coop buildings don't contemplate renting a portion of your home as in a roommate situation, but my experience tells me that they would object.
To learn more about the pros and cons of coop ownership, you might want to check-out this recent blog post:
I agree with most of the anwers, most co-ops require that the roomate, family member etc...be approved by the board. Imagine if the roomate turns into the roomate from hell, doesnt' pay rent, and refuses to move? It could be messy, co-op are geared to protect the best interest of their shareholders.
Coops drive me nuts, I suppose you need to have a spouse approved too? Lol but seriously, most coops I am familiar with would want approval, or would require them to be family. As mentioned above, just ask a board member, or check your bylaws.
There actually is no deed on a co-op. You own shares of a corporation. The corporation's board of directors makes the rules and they must be adhered to. You would need to check if the board allows you take someone in, because most co-ops must be owner-occupied. In fact when you purchase, the board always wants to meet anyone who will be living there.
check your charter/prospectus...each board is different. My personal prediction is that as long as they are not on the deed or renting from you, who you room with is your own business; but check your charter.