When doing a design I like to start at the core and work my way out. Design for the most critical things first (leave plenty of room for growth!) the work your way out.
Here are a few questions you will need to ask yourself:
-If I put a switch in the middle of each floor can I reach every workstation in 100 meters? If not where do the switches need to go?
-Can I run fiber between switch closets? It can run at 10/100/1000 and 10,000 Mbps so it can scale with your network and it is immune to EMI. Sometimes it is too expensive and you have to use cat5.
-When considering the campus, can you reach all buildings with MM fiber? SM fiber? Is their a high speed provider who can offer MPLS or SONET services? Otherwise you are down to looking at T1's and below. Don't forget point to point wireless if line of sight exists.
-Are there any gotcha's? Is there a reason that any workstation or server has to use an interface other than ethernet? (old token, twin-ax, etc)
There are a couple of things to get you started. If you post back some of your design thoughts I bet a few people here would have pointers for you.