We get called out to a fair number of pergolas that somebody else built, and the complaint is almost always the same: it looks great and it doesn't shade anything at the hour you want to sit outside. That's not a construction defect. It's a layout decision nobody made deliberately.
Shade from a pergola comes from the rafters, and rafters cast shade in a direction. Run them north to south and the shadow sweeps across the space through the day, giving you partial cover most of the afternoon. Run them east to west and you get dense shade at midday and almost nothing when the sun drops in the west — which, in an Alabama summer, is exactly the window you wanted the thing for.
So the first thing we do on a pergola visit is stand in the spot you plan to sit and look at where the sun comes from in late afternoon. Then we pick orientation, rafter depth, and rafter spacing to match. Deeper rafters on tighter centers block more sun at low angles, at the cost of more lumber and a heavier look. There's a real trade-off, and it's worth making on purpose.
Attached or freestanding is the next decision. Attached pergolas tie to the house, read as part of the architecture, and extend a patio you already use. Freestanding structures can go where the view is, which on a lot out toward New Market or the lake is often not against the back wall of the house.
If what you actually want is to be outside through a Valley August, say so early, because the honest recommendation may not be a pergola. A full covered patio with a solid roof, a finished ceiling, and a fan does something a pergola can't: real shade, dry when a storm rolls through, and ten to fifteen degrees cooler underneath. Plenty of people come to us for a pergola and leave with a roof, and almost nobody regrets it.
Whichever you build, set the post bases in concrete with standoff hardware so the end grain isn't sitting in water. Posts rot from the bottom, and a hidden standoff base is the difference between a structure that lasts twenty-five years and one that gets soft at the ground in eight.