Move all the planks into your recording space. You'll assemble the pieces, then fit them to the wall, so you need to make sure you can get them into the space once assembled.
Determine how your booth will fit in the room. You can create a free-standing booth in the middle of a room, build it into a corner, or completely convert an entire room. The configuration you choose will depend on the space you have available. A corner booth requires minimal materials, whereas a full room provides the greatest stability.
Join four of the planks together into a square, by placing them together at right-angles, then placing one of the plate brackets across the two ends like a bridge. Affix the plate to both planks by driving a screw through the holes in either end. Flip the square over and fit brackets in the same places on the opposite side.
Assemble three planks into a "U" shape, and join it to the square, creating a 6-foot by 3-foot rectangle with a horizontal support plank across the halfway point.
Repeat this process with the other planks, creating four independent walls.
Stand two of the wall frames up and place them at 90 degrees to one another. Join the two together using brackets at the top, bottom and in the middle. Repeat with the remaining two walls.
Affix one of the pairs of frames to the wall if you are building a corner booth. Otherwise, join the two pairs of frames together into a booth with a square footprint. Your booth is now ready to be covered with soundproofing material.