The evolution and structure of graphene layers on 4H-SiC(0001) and the corresponding interface are investigated by scanning tunneling microscopy (STM) and low energy electron diffraction (LEED). The surface is characterized by the so-called (6p3£6p3)R30± reconstruction, whose structural properties are still unclear but at the same time are crucial for the controlled growth of homogeneous high-quality large-terrace graphene surfaces. We analyse the properties of three phases in this reconstruction with periodicities (6p3£6p3)R30±, (6£6) and (5£5). Their LEED intensities strongly depend on the surface preparation procedure applied. The graphitization process imprints distinct features in the STM images as well as in the LEED spectra. An easy and practicable determination of the number of graphene layers is outlined by means of LEED intensities.