I texted a bit with William in Newark, he sent me links I will share. He is into wood working & pigeons, a good combination of interests for loft building. The initial ad you saw was for a very tiny structure. I'd use something like that for temporary situations like injury recovery, quarantine for new birds or breeding youngster from a specific pair. He does build a variety of sizes, though.
Also, if the pigeons are out & about flying alot, then a large building like I have, 12x24, may not be as necessary, but my pigeons are not flying free every single day, due to the numerous hawks here. Fall hawk migration is serious here, this is the migratory flyway. Pigeons do need exercise, though, they need to be able to fly, even if it's in the loft or protected pens. I believe more room is always better in general, for any creature we care for. My Pigeon lofts are 12x24 and 8x12, the 8x12 is for setting up particular pairs to hatch out their youngsters. Both lofts have predator & mouse proof flight pens, just as big, because some pigeons you won't necessarily want to fly freely, either because they'd fly back to their previous home, or they're too friendly & tame to evade or out maneuver a hawk attack, or they're just too valuable as breeders to risk losing.
There is a lot to learn if you're interested in these wonderful, amazing birds. Many have called them the race horses of the sky & military message saviors. Even if you do not plan to officially race them, I encourage you to read about & learn their capabilities, their history & their needs to care for them properly, so they'll be happy at your loft & want to stay home.
I've cared for several types of birds in my life, Finches, Macaws, Cockatiels, wild bird rescues, various types of Pigeons, Chickens, Guineas, Turkeys & even feed the buzzards at times. Pigeons hold a very special place in my heart. To know them is to love them.

You may want to look into the types of Pigeons there are. Some are more ornamental, not really good at flying, such as my Fantails. They still need some room to fly around inside a loft & in a large protected pen, but they may be better suited as pets, or even for showing, if that's what you're looking for.
Types of Pigeons
https://www.pigeonrescue.org/resources/types-of-pigeons/
Heroes
https://www.army.mil/article/30666/fine_feathered_friends
William sent me these links of his work, hutches & lofts, very nice work.
https://photos.app.goo.gl/SwN6ze1qHGJQRX3z8
https://photos.app.goo.gl/bYDwLeUmt5ZQjPjx8
A few pics of my place, still & always a work in progress. Let me tell you this...it is a labor of love, a daily commitment. Many seem to think that keeping pigeons will be easy, or they'll earn money flying pigeons at some events, but I can tell ya, you'll surely spend more than you earn, and you just might end up ticking off a family member, or significant other, by how much time you spend with the pigeons, so consider those aspects. Not everyone will have those scenarios, but some do, (I hear a fair share of nagging from time to time

).
Currently, I have Homing Pigeons and a few American Fantail Pigeons. I buy 50lb bags of feed, stored in rodent proof tins. I haven't raced recently, but I still band my youngsters, so if they happen to get attacked by hawks & someone finds one, they can be traced back to me. A few of my birds have survived hawk attacks, but most did need stitches. The 2 most recognized organizations are AU for racing & IF which includes fancy breeds.
https://www.pigeon.org/index.html
https://www.ifpigeon.com/about-the-if.html
Pics of my place, always room for improvement lol
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Hawk attack
I don't have pics of the one that's crop was literally sliced open, I stitched him up & he lived a ripe old age, though. Here is just a recent puncture wound. She came home a day later, I had to gently squeeze out this gelatinous blood & let the wound drain a few days while she recovered on amoxicillan in the bathtub. She healed up fine.
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