Epifanio, in the offical Wiki there is not much description. However there is more detailed descriptions of each Hold in the Linkmap in the Player Information forum.
_____________________
Under
Skyglow HoldThe rooms in the Skyglow arvintas are quite comfortable and have a bed, closet, work desk, and any other person effects the individual wants to put in. Each person gets their own room when they reach the age of thirteen unless they are married. In that case, they share a room with their spouse. Children sleep in an Arvinta common room at night until they are old enough for their own room.
Under
Skyglow ArvintaEach Arvinta consists of a communal meeting space and private rooms for the couples and adults. Children sleep in a shared room adjacent to their parents ...Each of Skyglow’s arvintas are situated along the exterior of the Hold and their common rooms have one wall made entirely of glass so the Vantha can always have access to the aurora for inspiration. The meeting space is also usually filled with the art of its residents,...Skyglow private rooms are also filled with their art....Upon marriage, Skyglow couples are given a bed frame with smooth sections on the head- and footboards. The couple will paint an image or scene on the smooth sections with their combined skill to represent their new unity.
_______________________
Under
Frostfawn HoldFrostfawn Hold was settled out into the trees...The Hold itself it very open on the inside to allow animals to move around freely. The Hold is quite large in order to hold all the animals and Vantha who are in the Hold.
Under
Frostfawn Arvinta Each Arvinta consists of a communal meeting space and private rooms for the couples and adults. Children sleep in a shared room adjacent to their parents...The communal spaces of these arvintas have hay covering the floor...The most common accessories in these communal rooms are pedestals of varying heights around the edges of the room that contain dishes of food for the various types of animals that roam the area...Their bed frames are very simple but also very tall. They purposely have their frames built on tall legs so that their various pets can sleep comfortably beneath
___________________
Under
Whitevine HoldThe hold has four stories. The two bottom most levels are for living spaces and each arvinta holds a family...The third floor is used for medical offices ...These rooms are outfitted as offices... The fourth level is for visiting patients that need to stay the night or need to have round the clock medical help. These rooms are just as good, if not better than the Whitevine personal rooms.
The Whitevine Arvinta Location is not set up yet.
______________________
Under
Iceglaze HoldThe Iceglaze Hold is a large building which is actually one of the least elaborate buildings in the city...The Hold is set up with rooms and living space on the ground floor with workshops either in the basement or out back in two person workspaces.
The Iceglaze Arvinta Location is not set up yet.
_____________________
Under
Coolwater HoldCoolwater Hold is right off the water. They have one of the smaller Holds but what it lacks in size it makes up in it's large docks...
Under
Coolwater ArvintaEach Arvinta consists of a communal meeting space and private rooms for the couples and adults. Children sleep in a shared room adjacent to their parents...This Hold decorates the communal space of their arvintas with interesting tidbits that wash up on shore as well as the skulls of large sea creatures that they’ve killed....When ships are retired for use Coolwater will usually pry off the boards that carried the ship’s name and hang them up in their communal spaces as well...In the arvinta private rooms individuals usually keep mementoes from their journeys out at sea...adults sleep in hammocks made of furs....
__________________________
Under
Snowsong HoldThe Hold is one of the smaller Holds but it has many rooms for teaching music...The Iceglaze hold took special care in building the Snowsong Hold. While other Holds did not need specially made rooms for acoustics Snowsong did. With this in mind all the rooms have fantastic acoustics.
The Snowsong Arvinta Location has not been set up yet
___________________________
Under
Winterflame HoldThe Hold is much like a large restaurant...The Hold is much warmer than the others
The Winterflame Arvinta Location has not been set up yet..
__________________
I know you probably didn't need all the information as you were probably asking about the overall architecture. In the Player Information forum there is one sentence that hints to one aspect of the holds, what they are made out of.
Each Hold forms its own cluster of buildings that are essential to the residents of that Hold while the city proper is a massive cluster that is located near the center. Most buildings are made from icestone and wood though some are made of stone while only a very few buildings are made with metal.
But again that is very broad.
________________
If looking at the images placed within each Linkmap location listed above, each picture looks like a large wooden lodge. I'm not sure how accurate this is, as you are correct, there really isn't much lore on this. I will give you my personal opinion, though, and maybe this can become another discussion.
In my mind at least I think of the holds as a bunch of really big igloos (made of Icestone of course) mashed together. In the middle of each hold is one HUGE igloo. This is the common area of each hold and houses the businesses that reside in the holds, such as the 'Aurora Showcase' of the Skyglow Hold. Other businesses that cant fit within their holds, such as the 'White Elk Stables' of the Frostfawn hold, are located directly outside and around their holds.
So there we have the huge, middle, common area of each hold. I then picture this huge igloo branching off into smaller, although still very large igloos, those are the arvintas. Each arvinta also has a common room, this is the large igloo. Branching out of the large igloo are small igloos that are the private rooms within each arvinta. So think of it as a huge tree that has bubbles for branches.
Here is an extremely horrible and crude representation of what I explained above:
Of course for some hold descriptions, like the Coolwater or Whitevine Holds where multiple stories and levels are mentioned this wouldnt work would it? Again this is simply how I picture it in my head.