Well, it depends on how elaborate you want to get. Martha Stewart grows her berries inside a gazebo like permanent screen house, and I believe she even puts orchard mason bees INSIDE during pollination time (I think the screen panels come off to allow bees in as well).

Those of us in the real world don't have the staff to do such project, as well as the finances! LOL!

What I did do for my 11 mature bushes was order a 20 x 100 foot piece of 40% knitted white shade cloth. It cost me about $350, but it will last for at least 20 years. With the number of berries I get (as many as 400 quarts in a really good year!), it's worth it.

I don't use any kind of a support or structure -- it's light enough that the bushes support it. I just pull it over the bushes and secure it at the ground with tent stakes.

And yes, if the birds where you live are like the ones here, you definitely need to cover the blackberries if you want to get any of them.

We have three low bushes and my husband hammered in four metal fence poles in a square, ran plastic-coated wire round the top, and then we came close to divorce as we struggled to cover the structure with the bird netting. We did manage to get it over the whole thing and stapled it to the ground, and we were able to get our first good crop from them.

Unfortunately, if you check out my other posting "Vanishing Blueberries" you will see that our luck did run out towards the end of the harvest and chipmunks have been fingered for the perps. I think we'll still cover them in the future, since we have marauding chickens from our neighbor's yard if we don't. You'd think they would at least leave us an egg or two in compensation.

Virginia in Virginia

If you live where blackberries grow wild in abundance, such as the Pacific Northwest, then you won't need to protect them from birds.

I am using 7 foot T posts to cage my blueberries. There is a rounded plastic cap you can get for the top an then run wire around and crossed. The rounded caps make it somewhat easier to put the netting on. The posts are about 5.5 feet high after you pound them in. The 15 foot netting I got isn't wide enough for my double row, so I over lapped by about a foot and a half and held in place with clothes pins attached to the wires and it seems to be working pretty well. You have to weigh it down at the bottom or the birds will push through. I just slip in through the overlapped area to pick.

I have found that if you just drape netting over the bushes the birds stand on top of the netting and peck through to the berries beneath. I live in the Pacific Northwest and my berries are at the top of the menu for the birds. I have built a "clothesline" to drape my net over. I staple two pieces of lathe together at the edges to keep the net on the ground.
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I am thinking for next year to build a box kind of structure out of pvc piping and duct taping the bird netting to it. Because the pvc is so light I should be able to tip it on it's side when I want to pick. Also I should be able to take it apart to store it in the garage when the blueberries are done.

I have done that. The PVC is so light that if you get a big wind you had better have it tied down or you get damage to your bushes and or frame.