If you want a particular shape, then just cleave and cut out the faces you want. Using the surface energies is for the case when you know the energies and want to see what shape that gives - your case is the opposite, you want a particular shape.
The cleaver should be very simple to use, on the first page you select 110 if that's what you want, then on the next page you select the side interfaces by dragging the arrows to make the correct cell shape, and third page you can skip, just click Create.
After that you can repeat it in X/Y (A/B) to make the cross section as large as you want, then add vacuum in Bulk>Lattice Parameters, then passivate with H atoms,
