Small helper class for generating dynamic dialog templates in memory and handling all alignment stuff. (see http://msdn.microsoft.com/en-us/library/windows/desktop/ff468828(v=vs.85).aspx)

DialogTemplate.cpp

DialogTemplate::DialogTemplate(const wchar_t * caption, u32 x, u32 y, u32 width, u32 height)
    : _size(0)
{
    Header header = { 0 };

    header.dlg.style = DS_SETFONT | DS_CENTER | WS_POPUP | WS_CAPTION;
    header.dlg.dwExtendedStyle = 0;
    
    header.dlg.x = x;
    header.dlg.y = y;
    header.dlg.cx = width;
    header.dlg.cy = height;

    header.dlg.cdit = 0;

    header.menu = 0x0000;
    header.className = 0x0000;

    append(header);
    appendString(caption);

    wchar_t font[] = L"Tahoma";
    WORD fontSize = 8;
    append(fontSize);
    appendString(font);
}

void DialogTemplate::button(const wchar_t * caption, u32 x, u32 y, u32 width, u32 height, WORD id)
{
    add(Button, caption, WS_TABSTOP | WS_CHILD | WS_VISIBLE, 0, x, y, width, height, id);
}

void DialogTemplate::groupbox(const wchar_t * caption, u32 x, u32 y, u32 width, u32 height, WORD id)
{
    add(Button, caption, BS_GROUPBOX | WS_TABSTOP | WS_CHILD | WS_VISIBLE, 0, x, y, width, height, id);
}

void DialogTemplate::editboxro(const wchar_t * caption, u32 x, u32 y, u32 width, u32 height, WORD id)
{
    add(Edit, caption, ES_AUTOHSCROLL | ES_READONLY | ES_LEFT | WS_BORDER | WS_CHILD | WS_VISIBLE, 0, x, y, width, height, id);
}

void DialogTemplate::text(const wchar_t * caption, u32 x, u32 y, u32 width, u32 height, WORD id)
{
    add(Static, caption, ES_LEFT | WS_CHILD | WS_VISIBLE, 0, x, y, width, height, id);
}

void DialogTemplate::add(WORD type, const  wchar_t * caption, DWORD style, DWORD styleEx, u32 x, u32 y, u32 width, u32 height, WORD id)
{
    Item item = { 0 };

    item.tpl.id = id;
    
    item.tpl.style = style;
    item.tpl.dwExtendedStyle = styleEx;
    
    item.tpl.x = x;
    item.tpl.y = y;
    item.tpl.cx = width;
    item.tpl.cy = height;

    item.preType = 0xFFFF;
    item.type = type;

    align(sizeof(DWORD));

    append(item);
    appendString(caption);

    WORD dummy = 0;
    append(dummy);

    Header * hdr = (Header *)&_buffer;
    hdr->dlg.cdit++;
}

void DialogTemplate::align(uint size)
{
    u32 pad = _size % size;
    if (0 != pad)
    {
        _size += pad;
    }
}

bool DialogTemplate::appendString(const wchar_t * str)
{
    size_t len = (::wcslen(str) + 1) * sizeof(wchar_t);
    return append(str, len);
}

template<class T>
bool DialogTemplate::append(const T & data)
{
    return append(&data, sizeof(T));
}

bool DialogTemplate::append(const void * data, uint len)
{
    bool result = 0 == ::memcpy_s(&_buffer[_size], BufferSize, data, len);
    _size += len;
    return result;
}

DLGTEMPLATE * DialogTemplate::get() const
{
    return (DLGTEMPLATE *)&_buffer;
}

DialogTemplate.h

class DialogTemplate
{
public:
    enum
    {
        BufferSize = 4096 * 16,
    };
    
    DialogTemplate(const wchar_t * caption, u32 x, u32 y, u32 width, u32 height);

    DLGTEMPLATE * get() const;

    void button(const wchar_t * caption, u32 x, u32 y, u32 width, u32 height, WORD id);
    void groupbox(const wchar_t * caption, u32 x, u32 y, u32 width, u32 height, WORD id);
    void editboxro(const wchar_t * caption, u32 x, u32 y, u32 width, u32 height, WORD id);
    void text(const wchar_t * caption, u32 x, u32 y, u32 width, u32 height, WORD id);

private:

    enum
    {
        Button = 0x0080,
        Edit = 0x0081,
        Static = 0x0082,
        ListBox = 0x0083,
        ScrollBar = 0x0084,
        ComboBox = 0x0085,
    };

    struct Header
    {
        DLGTEMPLATE dlg;
        WORD menu;
        WORD className;
    };

    struct Item
    {
        DLGITEMTEMPLATE tpl;
        WORD preType;
        WORD type;
    };

    void add(
        WORD type,
        const wchar_t * caption,
        DWORD style,
        DWORD styleEx,
        u32 x, u32 y,
        u32 width, u32 height,
        WORD id);

    void align(uint size);

    bool appendString(const wchar_t * str);

    template<class T>
    bool append(const T & data);
    bool append(const void * data, uint len);

private:
    u8 _buffer[BufferSize];
    uint _size;
};