The bilayer stacking sequence at the surface of SiC samples can be influenced by the preparation of superstructure phases as retrieved by quantitative low-energy electron diffraction (LEED). On 4H-SiC(0001) the preparation of a (root 3x root3)R30 degrees reconstruction under Si rich conditions increases the number of identically oriented bilayers in the topmost slab from two to three, thus breaking the 4H periodicity in favor of a more cubic type of stacking. In contrast, in a (2x2) phase on SiC(000 (1) over bar) the topmost bilayers are found be rotated by 60 degrees with respect to each other. This reconstruction obviously favors hexagonal stacking at the very surface. These surface bilayer arrangements may be viewed as potential seed for a polytype heterojunction.