For your office:
- benching for repairing machines with plenty of above bench power and live network sockets (THIS SHOULD NOT BE USED FOR STORAGE!!)
- separate storage cupboard/room allocated to IT (for all that toner, paper, etc which you will no doubt have to keep somewhere)
- storage drawers for useful things (power leads, spare laptop PSUs, network leads of different lengths, vga/dvi cables, etc)
- safe storage for tools and COSHH kit (make sure it is lockable so no-one can "borrow" stuff)
For the Server Room:
- walk round access for all cabinets
- space in front of cabinet to open doors and fully extend rack servers
- space behind cabinets to open doors and access cabling
- cabling routes either under floor or above cabinets on trays for safe access round room
- small desk/bench for when you HAVE to do some work in the server room - This should not be a permanent desk for someone!
- Small storage area (shelving) for network patch leads assuming core switching also in this room
- Over-spec cabinets. Separate cabinets for networking and servers, space for future additional equipment (you never know what may be asked for/required in 2 years), no more that 50% populated on day 1