The physical properties of an atmospheric boundary layer in Wolryong, a west coastal region of Jeju, South Korea, in terms of the atmospheric stability and roughness length, is important and relevant to both engineers and scientists. The study is aiming to understand the atmospheric stability around this region and its effect on the roughness length. We calculate the Monin-Obukhov length(L) against 3 typical regions of the atmospheric condition - unstable regime (-5<H/L<-0.2), neutral regime ($-0.2{leq}H/L{leq}0.2$) and stable regime (0.2<H/L<2), where H is e measurement height. The diurnal Monin-Obukhov length substantially varies in the night, but most of the H/L comes under the neutral regime. The roughness length scale can be derived by three different methods - logarithmic profile, standard deviation and gust factor method. The finding in the study is that the methods of the standard deviation and the gust factor, apart from the logarithmic profile, are all similar in terms of the roughness length under-the different atmospheric conditions. In addition, they have sufficiently shown the effect of obstacles and surface conditions around the measurement site.