I'm going to SFU currently, and we have a small ISP who provides residence with internet through a similar setup. Plus, I've looked at starting up an ISP (and done quite a bit of research/business plan) and know one person who runs an ISP. He suggested not doing it and mentioned that it is likely to be way more work than you think.
As has been mentioned, you will need to have someone available to do support, and, at least in Western Canada, we're used to having technical support available 24 hours a day. This was an issue with my ISP, because the internet would often go out after hours or on the weekend. Worst case, it went out on Thursday evening of a long weekend, and was out until Monday. So, support, as has been mentioned in this thread, costs. Either will cost you because you have to do it instead of something else or costs you because you have to hire someone else out to do it.
Next point is contention, which is a fancy way of saying how many people you can stuff down your pipe to the internet. My ISP is currently offering us (at least, that's the claim) of 10Mb/s downstream service. Now, they have roughly 1800 customers and 200Mb/s of bandwidth. So that's 1800*10/200=90. Which means that 90 people are fighting over the same bandwidth.
Which is way too high, and it shows anytime it gets busy, like latency jumping up to pings in the range of full seconds, huge packet loss, and speeds that make dialup look speedy. I would suggest something more like a 25-35:1 contention ratio. For the demographic up here, 25:1 would be better, you could probably get away with 35:1 or maybe even higher (but not too much higher, don't want to slow donw too much at peak). So, 35:1 for 175 people at 10Mb/s (seems like a standard speed) is 1.75Gb/s, which needs approxiamately 50Mb/s. A 39:1 contention ratio would be perfect for a T3/DS3/ or OC-1 connection at ~45Mb/s or ~50Mb/s. Should be enough, but it may not be depending on your user's usage patterns. You could consider getting a burstable connection, and setting your traffic shaper/router to burst if things are saturated for too long. Alternatively, get a metered connection and enforce transfer limits and charge people when they go over accordingly.
Also, as another point in the support vein, with that many people, you're going to need to do something better than tell people they owe you money. Billing will be important, and keep in mind the other costs that happen when running a business. Things like business licenses, GST registration and tracking, and other fun things like that.
Next point, and a technical one this time. Wireless is fine, if you do it well. Consumer routers, especially one per floor with more than a few people on them will not work. Most routers choke on more than five people at once. I would suggest not gong with consumer routers and get some proper commercial ones. Unfortunately, they won't be cheap. Also, WDS, unless run on a seperate frequency from the APs (dual band, say 2.4/5GHz or maybe proprietary 900MHz for the backhaul and 5GHz to farm out to your clients, or maybe even licensed spectrum, but that's probably too expensive. Also, 900MHz goes through walls and floors better) is not a good idea. Wire your APs to your core switch if you go that way.
I'd suggest wired ethernet for your client connections, if it isn't that hard to wire into the building. Remember, that (as someone else pointed out) does need to be up to code as well, which may mean an inspection. Wired allows greater bandwidth, and if you run Cat6, a few years down the road when you decide to offer 1Gb/s service, it's easier to upgrade to. Stick a switch in a convenient area, but keep in mind that you can only push normal ethernet cable to 100m (total) in length. You don't want to have your in wall length longer than about 95m (can't remember the official number, but you want to leave room for patches on each end to connect equipment).
Make sure you're using good managed switches for this, in case you need to whack someone's port for a virus flooding your network with traffic or something. Also, allows you to wire up every suite with ethernet, and enable the ports as people pay. If you want, you can also enforce your speed limits on the switches (assuming they're smart enough, not all are), but that could be better done on a router at your headend.
As was mentioned, you will have to police people just plugging a WAP into your network and then sharing it for free with the rest of the floor, as well as deal with possible interference from wireless devices if you go the wireless route.
Also, again, this has been mentioned, but you will have to make sure your users aren't doing things on your network that are illegal. Without breaking privacy laws yourself doing it. Is BT illegal? Of course not. But what happens when you get a complaint against a user (currently, privacy laws say that you shouldn't give the information out, but that doesn't stop whoever from trying to sue you)? What happens if all you've seen is encrypted communication? It's sort of hard to tell if that's a possibly copyright infringing movie or the lastest build of Fedora. Is it even up to you to police copyright? They may legitimately have accidentally dropped a DVD into the mess of cables behind the TV and had it get scratched up badly and are now downloading it to burn a new copy. So you may need legal council as well.
Also, are you thinking of offering value add services that other large ISPs provide? Things like email and webspace. You could run these on your own server, or farm them out. Hosting them with someone else is cheap, but then you also have to worry about their security and not just yours. Same thing goes with DNS. Are you going to run your own or just farm it out? Are you going to transparently proxy webpages to cut down on your outgoing bandwidth? It can really help (to the tune of roughly 6% for Shaw in my hometown), but it introduces new issues in administration.
And the router. Probably best to get something meant to do this rather than build your own, as big a fan of PFsense as I am, I'm not sure how well it scales. If you know PF really well, you could set up your own as well. A good Cisco/Juniper isn't cheap, and then you need to know how to use it or pay someone to come and use it for you.
And then you need to decide if you're going to block anything. Do you want the security issues from your customers by letting them run servers? Do you block incoming traffic to port 25/80/whatever? Are you even going to give your customers publically routable IP adresses or NAT your network off from the rest of the internet and deal with customers when they want to game/chat/whatever on the internet that requires a port mapping?
And once everything is up and running, how are you going to deal with things like abuse and billing? At some level, you will need to monitor your network to see how much bandwidth a user is using (depending on how you charge, you may charge $10/10GB and then $x per additional GB past that). And then what if someone is spoofing your router using ARP poisoning and intercepting people's personal data? You need to monitor a few other things as well to keep that (network abuse) from happening. However, people don't tend to like you watching what they're doing on their connection. I know I'm not a huge fan of my ISP(s) monitorring what I'm doing.
I can't think of anything more right now, but I'm sure I will at some point. Will add more then.
