Choose the type of wood you want to use to build your garden bridge. Depending on where you live you are going to want to choose lumber that is sturdy and that will withstand extreme temperature changes or heavy rains. Cedar, oak and redwood are all good choices.
Put your two 16-foot, 2 by 12 wood planks lengthwise on your shop table or workbench, and use your pencil and compass to trace the outline of the arch for the base of your garden bridge.
Use your circular saw to cut out the bottom and top portions of the wood planks that remain outside the lines you traced for your arch, making sure to cut the boards flat on the bottom of each end. Each flat portion should be about 18 inches long, acting as the "feet" for your arches.
Place the two arches three feet apart from each other and cut your 2 ny 4 wood planks about 1 inch wider than the width between the arches.
Lay one of 2 by 4s across one end of the arches and use your hammer to drive two nails through the top corner of each 2 by 4 and into the arches. Do this from one end to the other, spacing each wooden plank 1/8 inch apart, until the arches are completely covered.
Apply two coats of Olympic WaterGuard with your paintbrush to weatherproof your garden bridge. Allow the first coat to dry overnight before applying a second coat. Once the second coat dries, you will be ready to move your bridge into your backyard garden.
Place your bridge at the predetermined location in your garden. Lifting your new garden bridge will take help from a friend or family member, because it will be just long and wide enough to keep you from picking it up on your own.