Alpacas respect fencing, so the main fencing advice is to build fencing to keep out the predators you have in your area.  The alpacas will stay where you put them unless you leave the gate wide open.  Barbed wire is dangerous for crias and is not advised.  My favorite fencing is 5 foot no climb.  Many smaller pens are better.  This is so you can utilize rotational grazing and it will be easier to handle your alpacas.  It is preferable for your larger fields to narrow down to an area that two adults can easily catch the alpacas....a triangular field works well for this.  Feeding them in a smaller paddock will also acclimate them to coming in when you want them.  Trees and shade are always a good thing.

Shelters vary dramatically from luxury barns that look like people could live in them to three sided shelters costing less than $200 to construct.  The alpacas need shelter from the wind and rain - and sun if you don't have a lot of tree coverage.  It doesn't need to be that warm or air tight - just dry.  For inexpensive shelters, I have seen very nice 2X4, plywood, and plastic corrugated roofing for about $175 each.  Car ports are also effectively used with some plywood on the side.  I have even seen pig panels wrapped in tarps very effectively used for the side walls (tarps removed in the summer for increased ventilation).  They adapt well to old barns too - just as long as any dangerous objects are removed.  

Barn Design

If you are designing a barn from scratch, consider having stalls that open out to a small paddock under an overhang, and then another gate out to a pasture.  This multi-tiered approach will allow you the greatest flexibility for caring for and showing off your alpacas to visitors.  Below is my design for an alpaca barn.  I haven't built it yet, but one day I will.  The tractor area doubles as a shearing area or could be a large paddock.  Alpacas do better with corral panel stalls where they can see one another.

Sliding Door

Sliding Door

TRACTOR

FEED, SUPPLIES,

CHUTE, SCALES