  We consider the linear elliptic systems or equations in divergence form with
periodically oscillating coefficients. We prove the large-scale boundary
Lipschitz estimate for the weak solutions in domains satisfying the so-called
$\varepsilon$-scale flatness condition, which could be arbitrarily rough below
$\varepsilon$-scale. This particularly generalizes Kenig and Prange's work in
[32] and [33] by a quantitative approach.
