The Letter Pe has a number of different parts. The overall size should be 4X3 kulmusim. The Pe should have an upside down Vov at the top left end, and the head of the Vov should enter the face of the Pe. If you look closely, you shold see the outline of a Letter Beth (complete with its bottom heel) inside the empty part inside the Pe. It is because sofrim want so much to get this outline of the Beth in, that the letter is written slightly larger than the other letters. The space between the bottom of the upside down Vov and the top of the base of the bottom of the Pe should be 1/2 a kulmus, in order to assure that the Vov doesn't touch the bottom.