It is quite an undertaking, usually by a guild or individual with deep pockets and alot of land! I'm fortunate on Tahyang, McFly (I assume with friends?) built one in Marianople and the guild Conviction built one in Halcyona where fortunately I do own properties.
I missed the one going up in Marianople, but did attend (and contributed a couple of stone packs) to the guild Conviction erecting the Fellowship Plaza in Halcyona.
First step buying the plans. 500 Gilda Stars is alot of trade pack runs!
After you have the plans you need:
30 Stone Packs (each pack is 100 stone brick or 300 raw stone)
10 Iron Packs (each pack is 100 iron ingots or 300 iron ore)
10 Lumber Packs (each pack is 100 lumber or 300 logs)
The packs like all the housing have to be added in order. So, 30 stone packs have to be placed first.
Stone packs down, iron being added.
Iron in place and lumber going down
Completed Fellowship Plaza.
Conviction did a nice job placing this in Halcyona. It's next to their town hall with easy access for everyone in the area.
Making of the first specialty pack.
Most housing areas have crafting work stations, etc., but the specialty workbench only allows the production of a specific trade pack from that zone. (Ex. Marianople - Marianople Face Cream.) These trade packs do not fluctuate in terms of price based on turn in as only residents of that zone make them. So you're almost guaranteed the 130% return on a pack. (The ingame trade pack calculator is your friend for following percentage returns.)