1. Nail three saplings to a crosspiece
Form an arch with three smaller saplings nailed to a larger crosspiece.
2. Create the top fan
Find the middle of the crosspiece, and then gently bow the middle two pieces and nail them in place. Continue installing them in pairs. Check the spacing as you go, and then trim the ends.
3. Secure the two arches with a bottom crossbar
Create a doubled–up ridge and intermediate purlins. Nail the roof arches to the inside of the crossbar, to outside of the intermediate purlins and to one side of ridge.
4. Create the upright side pieces
Nail a group of saplings to the center crossbar. Then gently bend, evenly space and nail the ends in place. Position thicker ends near the bottom.
5. Screw the side pieces to the arched top
Attach the side pieces to the arched top with 3-1/2-in. galvanized drywall screws. Install 8-in.-long corner braces between the sides and top to add rigidity.
6. Mark the leg locations
Use spray paint to mark where you want to install the arbor legs. Then dig holes and install 18-in. lengths of perforated drain tile. Place a little gravel in each, set the arbor in position, level it, then fill with more gravel.