Building a piano stool all depends on the type of piano you have. The main consideration is whether the stool is for an older or newer piano. Newer pianos need stools with legs that range from 18 inches to 2-feet tall while older piano stools need legs that range from 2 to 2 1/2 feet tall. It is also important to measure the stool's height for the person who will be doing most of the sitting at it.
Measure the size of the piano stool and legs depending on the piano type and the shape desired for the stool. Most common shapes are circular or square. If there is one person who primarily will be sitting on the piano stool, it may be more comfortable to factor his height into the measuring process. After measuring, you can purchase a variety of wood types for your stool including oak, beech, cherry and maple.
Sand all pieces if needed. Drill holes into the four corners of the underside of the wooden base that will be the piano stool bench. Chisel the very top of the hole on the inside to make it just large enough to insert the screw head.
Chisel each screw head into the hole until secure on all four corners on the underside of the bench. Make sure the sharp point of the screw is poking out just enough from the hole so you can secure the piano stool legs to each one.
Take each piano leg and drill halfway down into the top of the leg where you will insert it onto the already attached screws in the sitting bench. Sand or trim away any excess splinters or ridges.
Insert a bit of wood glue inside the piano stool bench holes around the screw head. Do not put glue in all four holes at once, and add the glue directly before you insert the piano legs. As you attach the piano leg to the screws, slowly and carefully insert the emerged screw into the hole on the top of the leg.
Screw each leg securely and tightly until it is pressed against the bottom of the bench. Wipe away excess wood glue.
Let the piano stool dry standing straight up on the legs. If you decide to upholster the stool, first place the trimmed foam padding on the top of the bench. Screw it to the top of the bench with the small screws.
Trim the chosen upholstery fabric to the bench size. Make sure there is an extra inch on each side to overlap onto the stool sides and provide a place to secure the fabric. Use the remaining four smaller screws to secure the fabric to the sides of the piano stool in the four corners, folding excess fabric underneath. Trim away any excess fabric, but there should be none.
Varnish or stain the exposed wood, if desired.
Always be cautious when working with sharp objects such as screws, chisels and drills.