  Programmable metasurfaces have garnered significant attention as they confer
unprecedented control over the electromagnetic response of any surface. Such
feature has given rise to novel design paradigms such as Software-Defined
Metamaterials (SDM) and Reconfigurable Intelligent Surfaces (RIS) with multiple
groundbreaking applications. However, the development of programmable
metasurfaces tailored to the particularities of a potentially broad application
pool becomes a daunting task because the design space becomes remarkably large.
This paper aims to ease the design process by proposing a methodology that,
through a semi-analytical model of the metasurface response, allows to derive
performance scaling trends as functions of a representative set of design
variables. Although the methodology is amenable to any electromagnetic
functionality, this paper explores its use for the case of beam steering at 26
GHz for 5G applications. Conventional beam steering metrics are evaluated as
functions of the unit cell size, number of unit cell states, and metasurface
size for different incidence and reflection angles. It is shown that
metasurfaces 5$\lambda\times$5$\lambda$ or larger with unit cells of
$\lambda/3$ and four unit cell states ensure good performance overall. Further,
it is demonstrated that performance degrades significantly for angles larger
than $\theta > 60^o$ and that, to combat this, extra effort is needed in the
development of the unit cell. These performance trends, when combined with
power and cost models, will pave the way to optimal metasurface dimensioning.
