I think there are like 8 or so places that you can buy and collect money on. You have to be able to collect rent on 7 of the 8 places to get the final mission.

The one that I had to cheat on by using an online to guide to figure out was the strip club one. You have to go in the room in the back where a girl is dancing for you, and you have to literally watch her and spend like $1000 or so, which takes about 10-15 minutes to do... I simply went in the room, then make something to eat while it automatically paid her. Came back after eating, then voila, I owned the place.

Also, you have to do ALL the missions to own the place, so make sure you are done all the missions. Does that help?