Choose one of the following civilizations (others cannot have customized Home Cities): British, Dutch, French, Germans, Ottomans, Portuguese, Russians or Spanish
After levelling your Home City in Multiplayer/Skirmish you will unlock points to customize the appearance of your Home City.
To boost this super fast I found the quickest way was to setup a Skirmish match (any rules/map/players etc)
Then when you are in the game use the cheat Nova & Orion roughly 5/10 times in a row. Then hit ESC and choose RESIGN, YES, ESC, RESTART then YES.
You will see in the popups on the bottom of the screen that your city has leveled up. You will slowly level up your Home City (mine was going 2 - 3 times at the later levels).
Keep doing this until your Home City is around level 60 and you should have enough Customization points to get every upgrade. If you don't, just rinse and repeat a few levels until you have enough.