Adam Clarke on Jeremiah 36:2

Take thee a roll of a book - Take a sufficient quantity of parchment; cut and stitch it together, that it may make a roll on which to write the words that I have already spoken, that they may serve for a testimony to future generations. The Jewish rolls, several of which now lie before me, were made of vellum, or of sheep-skins dressed in the half-tanned or Basil manner. These were cut into certain lengths, and those parts were all stitched together, and rolled upon a roller. The matter was written on these skins in columns or pages. Sometimes two rollers are used, that as the matter is read from the roll in the left hand, the reader may coil it on the roller in his right. In this form the Pentateuch is written which is read in the synagogues.