The process and roll design for flexible roll forming of a U channel with varying cross-section was investigated. In order to obtain a constant leg height and variable cross-section width, rotational speeds, locations, orientations and dimensions of the rolls were calculated following the unfolding prediction of the sheet metal. The proposed methodology for variable cross-section open channels was tested by a case study conducted for a typical structural U channel of St 37 sheet steel with arbitrary dimensions. The appropriate pre-cut shape (unfolded blank) was calculated. The feasibility of the process and roll design was verified on a commercial roll forming design program COPRA RF coupled with a finite element module furnished by MSC Marc. Initial simulations yield not perfect, but promising results that the proposed process and roll design method is sufficiently powerful to program a computer numerically controlled flexible roll forming machine for a given open channel. Thus, the minor leg flare at the front and back ends and leg height variation along the channel can be eliminated by a few tryouts on the actual machine.