Considering that I only have one pen, this subject seems like a stupid thing to write about. I have not raised peafowl for 40 or so years. I have not had the experiance of building pen after pen after pen. I am not a large scale peafowl breeder. BUT, there are some things that I have learned the hard way with my one pen.
You have to get your materials right when building a pen. Sure you can be cheep and get lower quality materials, but that will also mean you will have to fix your pen every few years and eventually you will be paying more because your cheep materials don't last long and the expensive materials will usually last longer. So now let us take a look at the information that I have run into so far.
I use welded wire fencing. Many people seem to use the welded wire fencing and I like it. Evidently the welded wire fencing Tractor Supply makes is better than the stuff you can get at the Home Depot. Some welded wire seems to be of better quality than other welded wire, so make sure you get the better stuff. Some people like to use chicken wire. Chicken wire will rust quickly and can easily be chewed through by predators like raccoons and dogs. If you do use chicken wire, you might want to use plastic coated chicken wire which will last much longer. You could use chain link, but I think the holes in that would be too big. Something I didn't know to do for this first pen is to burry some of the fencing to help prevent animals from digging into the pen. That is another thing you want to think about. Make sure you use good posts for the fencing. I like using metal T posts and wooden posts for the corners.
Note that I am saying netting, not "pen top". DO NOT use fencing for the top of your pen. Peafowl do fly very well so you do need a top to your pen. I wanted to know more about why everyone says netting and you rarely see someone using say chicken wire for the top of their pen. The reason is because peafowl will litterally kill themselves if they fly up and hit a fence topped pen. Just recently a new peafowl owner had to put down her peacock because she was keeping him in a temporary pen that had a chainlink fence top. The peacock must have hit the top and she found him lying on the ground unable to stand. She had to put him down because his hip was broken in two places.
Anyways, I got my first netting off of ebay. I think the netting is too thin and it rips too easily. From some reading I have done, most people seem to recomend Toprite netting, 3T products netting, and Pacific Netting. For netting I think I will go with Toprite next time I get netting because of all the netting, this is the most recomended. Also normally you want knotted netting instead of knitted netting. If you live in an area with snow the 2 in. holes are better I think and they make very sturdy netting for snow areas. If you live in Florida like me, or some other place with a lot of sun, make sure you get something that has UV protection. If you can't find the right size netting for your pen, you can buy several sets of netting and usually on the same site you can buy things that are for attaching 2 nets together. Large scale pheasant breeders do this.
Do not let plants grow through your netting unless if you are sure that the plants won't do any harm to your netting. I thought that it would be pretty and natural looking to let the bamboo and young trees grow through the netting. For a few years it worked, but now the plants have ripped big holes in the netting to grow through it and have thus caused areas where the netting is too tight and areas where it is too slack. So I would say trim back the plants so that they are not growing through the netting.
Cover the posts that hold up the netting with something smooth that has no sharp edges. The posts will rub on the netting and tear it so using something like a plastic plant pot or a frisbee nailed to the post is a great way to protect your netting to save you money and grief.
Plan for expansion. When I got my first peafowl I didn't think about how many I would have in the future or how many pens I would have, where I would want the pens, etc. Make sure that you have plenty of room to have several pens side by side (to save costs on fencing). You might want all the pens near a water hose or near your barn or shed. You might want the pens close to your house so you can look out and see your peafowl, or you might the pens further away so that when the peacocks are calling it is not as noisy as it would be if they were right next to the house. Leave space for a vehicle to drive through so that if you just bought a new bird you can drive back and unload it from the vehicle and into a pen.
Make sure you use treated wood and or landscaped timber. I am not a wood expert, but evidently we used the wrong wood for my aviary and thus we need to replace some perches! Don't put yourself through that! Use the right wood the first time.
Another thing you should do is concrete the posts into the ground. For roosts you can make them many different ways. We use the cross method but soon started having issues with the horizontal part going crooked from the peafowl using it so much. Thus, you must brace the wood so that it is sturdy. Some people take a tree branch and treat it then use it as a natural perch. That is a neat idea as well. As long as it is ready for the elements.
Make sure that your peafowl have enough room to fly up and fly down from the roost.
The higher the roost, the better. You don't want your peacock's train touching the ground.
You can buy your own pen door or you can make your own. Some people make sure that the door is wide enough to get a wheelbarrow through it so that they can easily clean the pen.
Sometimes I have been in a hurry or forgetful and I forgot to close the pen door. Then the next day all the peafowl would be out and I would have to corral them all back into the pen. To help prevent that, you can attach a spring to your pen door so that it closes on its own.
You might even want to consider which way the door swings open. I have my door swing open to the outside of the pen and not to the inside.
Usually peafowl breeders make a tin shelter for their peafowl. If you want the peafowl to actually use the shelter at night, you might have to close them in there or put all of their roosts under the shelter. Peafowl will sleep outside even in a storm. For some reason they won't go sleep under their shelter at night, but will go in there durring the day if it is raining. So you can build them a nice big shelter and if you want them sleeping there only put roosts under the shelter. The shelter doesn't have to be super fancy, although it depends on how cold it gets where you are. You can have a metal roof and just fencing for the sides even.
Think about what direction you want the shelter facing so that wind won't blow inside of it and that perhaps it gets some good sun rays. Also, slanting the roof will help rain and leaves fall off of it.
You might even want to have a dim light inside the shelter or on the outside of it. You would use a dim light so as not to accidently make the breeding season come too soon.
To help prevent predator issues and things chewing through your netting, you should consider attaching hot wire around the perimiter of the pen or around the fence.
So plan everything out, make sure you get quality materials, and keep future expansion in mind. You can probably cut some corners, but be careful because you don't want to end up fixing the pen every 2-3 years. You want a good sturdy pen that will need little to no maintenence so that you can spend more time with your birds.
Most of these things I have learned the hard way, and I still need to do some fixing of my current pen as well as make more pens. Luckily, I am learning and will hopefully someday have building new pens down to a science. Right now, it is a daunting task!