Free pergola plans by ANA-WHITE.com
4 - 4x4 treated posts - 8-12 feet long (depending on how much of the posts you choose to bury or place in pier blocks)
16 - 2x2 @ 3 1/2" long (short cleats)
It is recommended that you cut boards as you go on this project.
Please read through the entire plan and all comments before beginning this project. It is also advisable to review the Getting Started Section. Take all necessary precautions to build safely and smartly. Work on a clean level surface, free of imperfections or debris. Always use straight boards. Check for square after each step. Always predrill holes before attaching with screws. Use glue with finish nails for a stronger hold. Wipe excess glue off bare wood for stained projects, as dried glue will not take stain. Be safe, have fun, and ask for help if you need it. Good luck!
So you first and foremost need to set the posts in the ground. Make sure you space the posts exactly as shown above, and that the posts are square (take diagonals). The posts need to stick out of the ground 107" - but you may need the posts to be longer if for example you are using buried pier blocks.
For this plan, you must have a tablesaw to rip boards with nice square edges. Rip your 1x8s down to 6 1/2" widths and use finish nails to attach to the cleats. The trim boards should be cut so that they hide the foundation. You could get extra fancy here and actually cover these posts in stone veneer as well.
The diagram above should read 22" of spacing between the boards. You will want to take a square of the project here (see step 1). When your diagonals match, rest two more 2x4s on top of the existing 2x4s, to the outsides. Screw to the posts as shown above. Then add the remaining 2x4s spaced 22" apart, using either brackets, pocket hole screws, or long screws carefully predrilled and countersunk from the top.
And this isn't what's done with the Pottery Barn one, but I'm a big believer in corner bracing. If you feel your pergola has any wobble or needs a little extra support, you can cut corner braces and screw on - you will be amazed at the difference the corner bracing does. Other means of "beefing up" the pergola (for example, high snow load or high winds) would be to use 2x6s boards instead of 2x4s and to notch out your boards) as done in the link given in the author notes.
It is always recommended to apply a test coat on a hidden area or scrap piece to ensure color evenness and adhesion. Use primer or wood conditioner as needed.