1) This all depends on the needs of the specific company that is looking at a campus enviornment.
2) I'll just throw out some basics.
Let's say you have 3 different buildings, each connected through fiber. Each building will have an access layer, which is generally responsible for connecting to end user machines, network printers etc etc. From the access layer, it will go
to the distribution layer which will provide aggregation (summarization if you want, ACL policies etc etc) from the distribution layer it will connected to the core layer.
Let's say each building had 10 2960 access switches per vlan, and each building has a distribution of a 3 switch 3750 stack, which then connected to the core of dual 6500 series switches running VSS. Now, this is just a basic template. Various other decisions will need to be made as well, such as redundant links, specific routing protocol you want to use, if you need to implement QoS for VoIP, or delay sensitive applications.
3) You can also have a datacenter and internet edge layers.
The datacenter layer will house all of your servers, ESX hosts if you have them etc etc. You will generally want very fast connections between devices within the data center.
Your Internet Edge layer will be the routers that you use to connect to the internet as well as other remote offices you may or may not have.
Once again, this is all very basic, and it all depends on who you are designing it for and there wants and wishes, as well as how much money they want to spend.
