I've ridden in a few indoor arenas. They mostly are all pretty much the same. Some of them the substrate is much better kept up meaning regularly dragging and watering the sand base to keep areas from getting hard and compact.
Some arenas are smaller than others but are mostly the same type of building, a metal sided structure with lights, often times mirrors and a smooth board around the outside of the riding area.
Some are huge like the above on that was located at Vantage Point Farms. Others like Lauries are still a really good size and have fantastic footing. I've always loved the smell of her arena after she's just watered it, very earthy!
The one that was located at Willy's barn was smaller in size and odd shaped because two corners were used as sitting areas and storage. Still it was a good space to ride in, something that would be more affordable if I need to build one on a future property.
I enjoy the large on at Whispering Winds Farm. There is a enough room for multiple riders to work in the arena and they do drag and maintain the substrate pretty regularly. I like being out of the wind and cold or bad footing during winter. I hope I can have on when I have acerage because it lets you ride when ever you want.