documentclass - switched to final, use symmetric margins for oneside

        marginparsep=0.3cm,

    }{geometry}

}{

    % set final margins

    % set final margins depending on oneside or twoside

    \makeatletter

    \ifthenelse{\boolean{@twoside}}{%

        % twoside=true

        \PassOptionsToPackage{

            outer=2cm,

            inner=3cm,

        }{geometry}

    }{

        % twoside=false

        \PassOptionsToPackage{

            lmargin=2.5cm,

            rmargin=2.5cm,

        }{geometry}

    }

    \makeatother

}

\usepackage[

    vmargin=2cm,

% TODO: switch to final and twoside before printing

\documentclass[a4paper, 11pt, draft, oneside]{memoir}

% TODO: switch to twoside for printing

%\documentclass[a4paper, 11pt, draft, oneside]{memoir}

\documentclass[a4paper, 11pt, final, oneside]{memoir}

%\documentclass[a4paper, 11pt, final, twoside]{memoir}

\input{header}