The average handyman can easily build a picnic table. Inexpensive components in standard sizes are all readily available at builders' supply stores. Treated pine is a popular wood choice for outdoor furniture as it will resist both weathering and termites. You can also choose cedar or redwood, but be aware that these cost more. In the end, you can't underestimate the usefulness of a good picnic table -- especially one you've constructed yourself. Not only are they built for durability, but you'll be glad you have one when you're entertaining a large crowd.
To make the table top, cut one of the 2x4s into three pieces, each 26 inches long. These are the cross pieces that will support the table top. Lay them out standing on their sides, then use a tape measure to position the center cross piece exactly 4 feet from each end -- this will be the middle of the table top. Lay the 2x4 table top boards on them at 90-degree angles -- the boards should extend 4 inches beyond the cross pieces at each end. Nail them together.
Make the four legs out of two of the 2x6 planks. Each leg should be 33.5 inches long. Cut each end to a 60-degree angle -- you'll need to use a protractor or a miter saw to get the angle right. Cut the other two 2x6 planks so that each is 5 feet long.
Turn the table top upside down to attach the legs to the outside of the cross boards. Align the legs flush with the table top so they extend exactly over each exterior corner of a cross board. Drill two holes in each leg and bolt together. Countersink the inside of the cross boards and insert the bolts so that the nuts are on the inside. Bolt the 5-foot stretchers to the outsides of the legs using two bolts per leg and countersink the nuts.
Cut two 2x4 braces per side to 44 inches long with a 17-degree angle at each end where they will meet at either side of the center cross board and also at the stretchers. Nail to the cross board and nail them to the seat stretchers, adjusting the angle if necessary to make certain the table is square.
Turn the table right side up and nail a 2x4 seat support between the seat stretchers on each side of the table. Measure the table and make sure the legs are all square then nail the 2x10 seats onto the seat stretchers and above the seat support. Sand the wood smooth to prevent splinters and finish with a stain and/or wood sealer.