These are the measurements I used:
Cover - 19cm long x 15cm wide
Inside pages - 17.5cm long x 14cm wide
Tab closure - 6cm long x 3.5cm wide
Instructions:
1. Fold the cover and each page in half and iron the crease.
2. Place the pages inside each other and then inside the cover.
3. Once they are neatly stacked like the finished book, secure with pins through all the thicknesses. This is to stop them moving while you do the blanket stitch binding.
4. Do the blanket stitch binding.
5. Trim one end of the tab closure rectangle to whatever you prefer - I have notched the corners like an office supply label. You could round it also or leave it rectangular.
6. Stitch the untrimmed end to the inside middle of the back cover.
7. I used a decorative flower cutout and button to brighten mine up and then stitched a press stud to the underside. You could leave yours plain or you could stitch a button to the cover and cut a slit in the tab closure to close it. Just use whatever option you prefer.