Sidewalls are wooden or concrete and are either 4 or 6 feet tall. Reflective tarps are used to reflect solar radiation to prevent over-heating. Hoops wider than 38 generally use trusses rather than the tubing used on narrower hoops. Some companies make hoops as wide as 75 . The north end is generally closed during winter except a small area for ventilation.
Various ends are available.
This one uses tracks, much like a garage door, but it needs more open space for ventilation. Hoops are often used for finishing pigs. Plentiful, high quality deep bedding is the key. Sow gestation is another common use for hoops. Sow feeding is an important decision.