Also, you will have to look at this from the access standpoint. If you are broadcasting wireless for an apartment building, unless you use special signal blockers on the outside corners of the building, then ANYONE can use this system without even being charged rent, services, or other. I will tell you this, it sounds to me like you are getting yourself into a WHOLE BOATLOAD more than you are anticipating. I understand that you have the entire business sense of this thing under control, but when it comes to the technical side, you are looking at broadcasting wireless signal accross a large area, and then having to set the filter to allow only paying customers. This boils down to pretty much 2 technologies. You could consider the idea of using an encryption method, but then a tennant has a buddy and says, "Oh, well uh, they just told me to put this in and it worked...", then the buddy is getting your wireless. Or the other option would be to set the MAC filters to only allow the MAC addresses of the tennants that give you their MAC address. That would be more likely to do, but in a large set of buildings, you would have to make sure that each customer would have the access to the closest/strongest access point. Or, if you wanted to be mobile around the complex, enter the MAC addresses of each customer, into each filter so they could pick up any of them. Even with all that aside, you would have to worry about someone installing their own wireless access point or router to set up their own little LAN in their apartment. Ok, if an IP address scheme comes into play that is incorrect because of user, or of another tennant starts picking up their network instead of yours, then you have customer complaints all day long.
I apologize for the ramble, but that is only a very small portion of the work you will be putting into a project of that sort.