Well I'll start the list off
1. You need to identify what many rooms and many uses are likely to be commercial/office/retail/manufacturing etc
2. You will need to know how the system is going to be payed for, ie individual meters, or just the one upfront one
3. I assume the system is 3 phase, you will need to know what is going where to distribute the phases
4. You will need to sort out communal areas from business areas, or is this just one company taking over the whole building
5. Type of containment which will depend on your use, environment
6. Things like false ceilings, raised flooring, will determine what you use.
7. Lighting what kind of lighting. Warehouse lighting is different from office lighting is different from a manufacturing process lighting you will need some indication
8 Power again as above all different areas will require different solutions, will there be need of 3 phase supplies for equipment, will there be need of 16amp sockets are you going to use RFC or Radials
9. Personally I would not go down the route if I were you on alarms or emergency lighting, if this is you first "test the water" project stick with LV side of things
10. You could though design out of fun, DATA systems. CCTV systems Access control systems
There's a start for you