For a competent woodworker with the right tools in the garage, an octave mandola can be a great first step into the world of luthiery. The instrument is quite a bit larger than the mandolin, though it can be made to different scales. The usual mandolin scale is 13 and 7/8 inches but a good scale for an octave mandola is 21¾ inches adding resonance to the deeper tones.
Pencil the outline of plans for the mandola's neck and body onto pieces of plywood, and with the band saw cut carefully following the pencil line. Find plans online, or as part of a purchased kit. Follow the specifications for each instrument part. Choose plans for the 21¾ inches scale.
Trace the neck template from Step 1 onto wood blank. Follow the pencil line with the band saw, cutting first from headstock toward heel block. Pay special attention to the heel block, where the neck connects to the body, because a sloppy cut will lead to a weak fit between neck and body and could cause tuning problems later. Chisel grooves for frets following plan measurements.
Trace the body template onto wood blanks for top and bottom, and cut with the band saw. Carve the arch into the top and bottom with the finger-planes, making sure to keep the form as symmetrical as possible. Cut x-bracing with the band saw to match the arch of the carved top and bottom, and sand until the fit is snug. Trace the sound hole from the plans to the carved top board and cut by drilling a small hole and following the line with a jigsaw.
Shape the sides of the mandola. Cut side wood to shape and proper thinness, usually around 1/10 inch, and dip in water. Bend sides on a heated bending pipe until they match the plan. Create lining by which the top and bottom will be attached to the sides, by partially cutting twin strips of wood every 1/4 inch, and glue into place using clothespins as clamps.
Glue the sides to the neck block. Cut neck block to match dovetail created on the heel block in the step 2. Sand the joint until there is a snug fit.
Attach the top and bottom to the lining of sides with glue. Glue dovetail joint from heel block to neck block on body. Glue finger board onto neck. Glue bridge to the top board, following plans. Clamp all parts together until dry. Sand off excess glue.
Paint or varnish and add hardware . Add the tail piece, tuners, the frets. Install a pick guard if desired.
Guide strings through the tail piece, up the fretboard and through the tuners. Wind the tuners until the string is in tune, compared to a piano or a guitar tuner. Tune the strings to C D G A, top to bottom.
If you have a speaker and a tone generator, you can test the tuning of the top and bottom pieces by setting them on the speaker and changing the tone on the generator. Throw sawdust onto the boards and look for the Chladni lines to form.
Careful if you choose very hard woods to build your top and bottom pieces. They can catch fire when sawing.