City Example: [Tier 3] Atlantis

Tier 1
Town square
Roads
Street signs
Planned living plots

Tier 2
Town Hall
Town Storage (With public chests, stocked)
Crafting Hall
Blacksmith room
Smeltery
Public crop farms
Public mine
Tavern / Restaurant
Map room with at least 9 maps
Non-torch lighting

Tier 3
Banners
1 Shop
Library + Complete Lv. 30 enchanting room
Brewing room
City walls - not made of cobblestone
Public animal farm
Tree farm
Stables
Town jail
Inn or Lodge
Nether portal
Lighthouse (if next to an ocean)

Tier 4
A grand entranceway
Art museum/gallery
Road in the nether to the nearest nether fortress
Vineyard
Guard Tower
Barracks
PvP Arena
Bank or vault
Inn/Lodge must have 10 beds
Tree farm must have every type of tree
Minecart rails along roads
Trade outpost (Shops in an area other than your town)
River or other natural water source (mountain spring, oasis, lake, ocean, ..) within 20 blocks of the city limits
Fishing hut
Water mill

Tier 5
Villagers and houses for them
Embassy for other towns
Observatory
Must have a farm for every crop and animal
Wheat
Melon
Pumpkin
Sugar Cane
Potato
Carrot
Cocoa Beans
Beetroot
Nether Wart

Chicken
Cow
Pig
Sheep

2 Public works (i.e: statue, fountains, arenas, giant temple)
Port with boats and docks (if near a river or ocean)
Subway or other connection to nearest public area
A castle or large structure to establish power
A town attraction - Something large and unique that engages players (Spleef arena, casino, archery range, BE CREATIVE)
A full-size beacon
Marketplace