The pits and Si regrowth islands that form during the roughening of Si(100) by Cl at 700 K have characteristic patterns that depend on the amount of adsorbed Cl, suggesting the importance of adsorbate-adsorbate steric repulsive interactions. Monte Carlo simulations of roughening focused on those interactions. While the resulting morphology resembles those observed at intermediate coverage, the inability of the simulations to reproduce the experiment results at low coverage indicates that other interactions must be considered, including strain anisotropies that would favor the formation of large features.