I will present a detailed discussion about how to use Sunyaev-
Zel'dovich galaxy cluster counts to extract cosmological parameters.
A particular emphasize will be given on the systematic errors, such
as scatter and uncertainty in the limiting mass and how to improve
the constraints by complimentary cluster observations such as weak
lensing with the Dark Energy Survey (DES). I will present
degeneracies between astrophysical and cosmological parameters and
briefly discuss other systematics such as point source confusion and
CMB noise.