I finally made myself a book cover for my music which is just plain black and makes it perfect for concerts. The pattern is super easy.
--- This tutorial is free but for your convenience I decided to offer the complete tutorial as a PDF for download for only $2, if you prefer to have everything in one structured document ---
Therefore open the cover of the book and measure in from the edge for a little bit more than half the width of the page, in my case it is about 4.5". Again add two lots of seam allowance and for the length use the same measurements as for the main body parts (including seam allowance). This would make it 11.5 x 5.5". Cut four of them.
Interface the four sleeve parts with fusible interfacing.
Put two of them right sides together and sew along on of the long edges. Turn right side out, press and topstitch along this edge. Repeat with the remaining two sleeve parts:
Repeat with the other sleeve part on the right hand side of the main body part:
Take the other main body part (which will be the exterior body part) and interface it with heavy stabilizer to add more strength. The heavy stabilizer should not lie on the seam allowances, so before ironing it down cut off 0.5" (1,25 cm) on either side.
Place the interfaced main body part right side up and put the interior body part with the sleeves on top of it, right sides together. Make sure all the edges are aligned. Pin in place and stitch all aroung the edges, but leave an opening of about 4" (10 cm) at the bottom center.
Trim down the seam allowance to reduce bulk and clip the corners.
Turn the book cover right side out through the opening. Make sure to poke out the corners and then iron is to make it nice and flat.
At the opening fold the seam allowances down to the inside and topstitch it close.