As a general rule, alapcas need at minimum a 3 sided shelter that will allow them a space to escape from inclement weather or the hot sun. There should be enough room for all the alpacas in the pasture to kush comfortably and not invade the personal space of the other alpacas in the shelter. There should also be room for a hay feeder, weather it be on the wall or the ground, and a bucket of water.
Alpacas have very little in the way of defense mechanisms other than to out-run their predators. For this reason a good strong fence structure is more to keep predators out rather than alpacas in. An alpaca will very rarely challenge a fence. The exception to this being the breeding male who is trying to get over the fence to some open females. They have been known to jump over a 5ft fence.
5ft 2″x4″ no-climb fencing is the most recommended. This fences should be stretched out and secured to wood posts that are securely cemented into the ground. T-posts can be used intermittently on interior fences with a wood post after every 2 – 3 T-post. Additionally you should use a hot wire fence on the top and bottom on the OUTSIDE to deter digging and climbing of predators. The most cause of death from predators in the United States is neighborhood dog packs or coyotes.