We investigate dependence of Charnock parameters and nondimensional roughness length (z_o/H_a) on wave age. A roughness scheme is developed which reflects sea state. Effects of wind fetch, duration and water depth on sea roughness are studied. Sensitivity of roughness to friction velocity and wave age is discussed. The scheme is applied to the latest COARE algorithm. With data of FPN platform in North Sea in December 1985, applicability of the new scheme is tested. It is shown that TY01 and 002 schemes overestimate u. and YT96 scheme underestimates it. Results of the new scheme are the closest to observed data.