|This isn't a "simple" setup no matter which way you slice it.|
As a professional I'm going to tell you this. If you contracted me to consult and come up with a plan for you, I would come and do some testing and examine the building physically. It would then take me a couple days worth of work to come up with the optimal setup. The consultation and plan would cost you thousands of dollars because in order to do it right and give you the best, most cost effective plan would take a lot of work, testing and skull sweat. Which is to say, it would take time and time is money.
Then you'd have to either pay more to have the install and setup done, or do it yourself. It's obvious from your post and subsequent responses that you don't have the knowledge to do this yourself and have it done right so in the end, you'd have to pay somebody.
Once in place and working, you then become responsible for providing support for your tenants. This means they can call you anytime. You can't just not answer because as their internet provider, they have an expectation that should something go wrong, you'll get on it immediately and get it fixed. So, unless you want a bunch of pissed off neighbors, you'd have to drop whatever you're doing (like working, eating, sleeping, having sex.......etc etc) to address their issues.
Keep in mind, they'll be calling you about everything even if it's not related to the internet you're providing. (ie: "My computer won't start, what's up with that?", or "My sound stopped working" etc etc)
Oh, one other thing too. Chances are that most, if not all, the other tenants in this building who want internet already have it. Why would they swap what they have for your service? If they have any knowledge at all they'll know their highspeed setup is going to be a lot faster than yours since your's is wireless and has a bunch of other people sharing it. I know if I was living in your building and you asked me if I was interested you'd get "NO" for an answer.
I noticed you very carefully didn't say, "I own the building" or "I am the manager" which means you're a tenant. As such this means you have no legal right to place any equipment of any kind anywhere in the owners building period end of story.
If you have some grenadiose plan to charge the tenants then you are a business and that would require you to have a business license and other legal considerations (ie: you'll want to incorporate which costs money or the first time you get sued, and you will get sued, you'll end up losing your shirt and spending the rest of your life working for someone else)
Even if you are the manager, you can't just do what you want without the owners permission.
All in all.............this is an idea that's just not worth the time and hassle.
You do what you want but I can guaratee if you do try to do this, you will end up wishing you hadn't.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.