It seems like you are actually starting a LAN (Local Area Network) in your apartment. WAN's span across multiple locations. In esssence, a WAN is similar to two or more LANs that are connected. While I reccomend taking the advice of the others and getting professional help, I will give you an idea of what you need to get started. First thing you mostl likely will need is a data closet or somewhere to house all this equipment. Since you will have up to 80 apartments connecting, I think your best bet would be to get a patch panel hooked up in this closet. The patch panel will have wires that run from every room all the way to the closet. Next you will need a switch and a router. The router is the equipment that actually manages the network routing (data flow). You will connect the switch to the router. This activates the switch. (side note: Make sure the switch is autosensing, you dont want to have to deal with crossover cables and other such headaches, but most are now anyway) With 80 rooms connecting, you will probably need multiple switches. You will need enough to have 1 port per room, or at least 80 ports. A good idea here is to make sure the patch panel is numbered according to the apartment numbers. It will make the job alot easier. Now, whenever you want to make an apartment room active, simple plug a patch cord into the patch panel port with the corresponding room number and connect it to the switch. This should make the port live. Finally, you will need a broadband modem from your ISP (internet service provider). Hook the modem up to the router in the internet port (labled as such). This will give your network internet access.
Now, this is a simple overview of what needs to be done. There is so much more involved than this, as the others were trying to let you know. Cable will need to be run to every apartment back to the panel. If your using standard internet methods, your network is going to instantly eat up its bandwidth and no one will be able to enjoy the internet. If your serious about supplying your tenants with internet access then you will want to purchase a T1 line. This will most likely go through your phone company. Once you get this apartment done you can move on to the next. There is an easier and more efficient route, and that is wireless. You can setup a wireless network and need much less equipment. You will need the modem and a wireless router along with some wireless access points installed (several on every floor of the apartment) Then each of your tenants will need to buy a Wireless Network Adapter. There are different types and they vary with laptops and desktops.
I must ask what your purpose is. If it is simply to provide your tenants with internet access, then you will not need a WAN, just a LAN at each location. If you are wanting to network your apartment complexes for business aspects, then you really need to seek professional help. Eitherway, it woul dbe a good idea to get a professional to handel the work.
Good Luck]
Hope this helps