Bug 33550 [Dialogs] Dialog should support remembering size and position
There are several dialogs that remember its size and position. Since restore the size and considering screen size and font changes isn't trivial JFace's Dialog class should support remembering and restoring size and position. These would realy ease the task for subclasses. May be you can steel the code from OpenTypeSelectionDialog.
bundles/org.eclipse.jface/src/org/eclipse/jface/dialogs/Dialog.java
* Get the default font for this type of control.
     * 
     * @param control
     * @return the default font
     */
    private static Font getDefaultFont(Control control) {
        String fontName = "DEFAULT_FONT_" + control.getClass().getName(); 
        if (JFaceResources.getFontRegistry().hasValueFor(fontName))
            return JFaceResources.getFontRegistry().get(fontName);
        Font cached = control.getFont();
        control.setFont(null);
        Font defaultFont = control.getFont();
        control.setFont(cached);
        JFaceResources.getFontRegistry().put(fontName,
                defaultFont.getFontData());
        return defaultFont;
    }
    /**
     * Return whether or not the dialog font is currently the same as the
     * default font.
     * 
     * @return boolean if the two are the same
     */
    protected static boolean dialogFontIsDefault() {
        FontData[] dialogFontData = JFaceResources.getFontRegistry()
                .getFontData(JFaceResources.DIALOG_FONT);
        FontData[] defaultFontData = JFaceResources.getFontRegistry()
                .getFontData(JFaceResources.DEFAULT_FONT);
        return Arrays.equals(dialogFontData, defaultFontData);
    }