Back to Basics
The writer obviously moves in better circles that I do. From past experience, the following still needs to be pointed out far too often:
1. A cloak room is not a server room, even if you put servers inside.
2. You cannot power 100A worth of equipment from a 16A wall socket. Not even if there are 2 of them.
3. You cannot cool the above by opening a window and puting two fans in front of the computers. A domestic AirCon unit won't do much good either. Also, don't put drippy things above sparky things.
4. Ground lines are not for decoration. They need to be used and tested regularly for safety.
5. DIY plugs cannot be wired any which way. Not even in countries that allow Line and Neutral to be swaped.
6. The circuit breakers at the end of your circuits are part of your installation.
7. You cannot protect a rack of equipment with a UPS from PC World. If you really need this, you're going to have to buy something which is very big, expensive and very very heavy. And the battaries are only good for 3 to 5 years.
8. Buildings have structural limits. You cannot put several tonnes of densely packed metal just anywere. Know your point and rolling loads and then check the building.
9. Electrical fires are nasty. Chemical fires are worse. You need stuff to protect the installation.
10. If you want 24h service, you'll need 24h staffing. A guy that "does computers for us" won't do.
11. A 1 Gbps uplink cannot feed 48 non-blocking 1 Gbps ports.
12. Metered and managed PDUs will save you bacon one day. Buy them.
13. Label all the cables BEFORE installing them. (No, you cannot just "follow the cable" afterwards)
14. My favourite: Don't blow your entire equipment grant on computers. All the stuff avove costs money.
And that's just off the top of mehead.