Elaborate pergolas made from expensive lumber or other materials can cost thousands of dollars, but you can build a less expensive pergola by sticking to a simple design and using inexpensive lumber. Regardless of cost, a simple pergola can provide subtle shade and help define an area in a garden. Pine is typically a cost-effective lumber option, but you also can save money by building with salvaged or reclaimed lumber. If you have the proper tools and a wooded lot, you can cut your own timber and rip it into boards for free, or build the pergola from unfinished logs.
Setting Upright Posts
Drive stakes in the ground and tie string lines to layout a square or rectangular space for the pergola. Check the corners with a framing square to ensure each corner is a perfect 90-degree angle. Keep the size of the pergola minimal to make the structure as inexpensive as possible.
Spray an "X" at each corner with landscaping spray paint to mark the location for the pergola's posts. Additional posts might be necessary along the sides between the corner posts; no more than 6 feet of space should be between any two posts.
Dig a hole 30 inches deep at each sprayed "X" mark, using a manual or electrical post-hole digger. Each post hole should be 1 to 2 inches larger in diameter than the post diameter. Posts for pergolas typically measure 4 by 4 inches or 6 by 6 inches in width, and larger posts increase the pergola's cost. The posts' height should be equal to the desired height of the pergola plus 30 inches. Although the height depends upon your preference, 8 feet is a typical pergola height.
Set a post in each post hole, hold a carpenter's level against the sides of the posts and make adjustments until the posts are perfectly vertical, or plumb. Screw a 2-by-4-inch piece of lumber to the side of each post, running it diagonally to the ground to brace the post's position. Fill the post holes with dry, fast-setting concrete mix, and pour water in the holes until the concrete is wet. Some concrete products must be mixed with water before adding those products to holes, however; follow your concrete product's package directions. Allow about 1 hour for the concrete to set in the holes before removing the 2-by-4-inch lumber braces.
Attaching Horizontal Supports
Measure the distance from outside edge to outside edge of the corner posts on one side of the pergola and on the side directly opposite that side. Add 24 inches to that measurement, allowing for 12 inches of overhang for each horizontal support beam. Measure the two sides according to your preference in rafter direction because the support beams will run perpendicular to the pergola rafter beams.
Cut four pieces of 2-by-6-inch lumber to the measurement for the pergola sides plus 24 inches. The cut pieces will be used as horizontal support beams. The two posts on each side of the pergola will be sandwiched between two horizontal beams. Cut decorative notches at each end of these boards if desired, placing a large can or bucket at the ends of the boards and using it as a guide to trace the curved design then cutting out the curved design with a jigsaw.
Position one 2-by-6-inch horizontal support beam on the outside of a set of posts, lining up the top edge of the beam with the tops of the posts and leaving 12 inches of the beam overhanging each post. Lay the carpenter's level across the beam, and make adjustments until it is level, cutting excess wood from the top of the posts with a reciprocating saw if necessary. Drive four evenly spaced 4-inch-long decking screws through each end of the support beam and into each post.
Position a second support beam on the outside of the second set of posts. Lay a scrap board across this second support beam and the previously installed support beam. Lay the carpenter's level on the scrap board, and adjust the position of the second support beam until it is perfectly level. Attach the second support beam with a series of four evenly spaced 4-inch-long decking screws driven into each post.
Position the third and fourth horizontal support beams on the inside of each set of posts, lining them up with the previously installed support beams on the outside of the posts. Drive four evenly spaced 4-inch-long decking screws through the beams and into each post.
Laying Rafter Boards
Measure the distance from the outside edge of the horizontal support beam installed on one end of the pergola to the outside edge of the horizontal support beam installed on the pergola's other end. Add 12 inches to that measurement. Cut 2-by-4-inch lumber to make several boards that total measurement, cutting a decorative curve at each end of them if desired. These boards will be rafter beams for the pergola's roof. Using 2-by-6-inch lumber provides a more substantial look but increases the pergola's cost.
Mark the center of each horizontal support beam that is installed on the pergola, using a pencil to make the marks. Mark each horizontal support beam 16 to 24 inches in both directions from the center mark you put on each beam to the pergola's posts, and place those new marks at the exact middle along each beam. These 16- to 24-inch measurements mark the positions for the rafter beams. The spacing you use depends on personal preference and what you think would look best considering the length of the horizontal support beams and the pergola's size.
Lay one rafter beam perpendicular across the horizontal support beams, placing the rafter beam on its narrow edge and lining up that edge's center with the pencil marks on each horizontal support beam. Each end of the rafter beam will overhang the pergola by 6 inches. Drive a 4-inch-long decking screw at a downward angle through the rafter beam and into one of the horizontal support beams below it. Repeat the procedure with a second screw on the opposite side of the rafter beam, driving the screw into the same horizontal support beam below. Repeat this attachment process with the remaining three horizontal support beams, using a total of eight screws to secure the rafter beam in place.
Lay the remaining rafter beams in position across the top of the horizontal support beams, lining up the rafter beams with the pencil marks that are on the horizontal support beams. Drive two screws through each rafter beam and into each horizontal support beam at each place where the beams meet.