Hi Allahbaksh,
what are you looking for exactly?
A library for GWT to develop Windows 8 native applications via the JavaScript projections or something to make Windows 8 lookalike web apps?
First isn't possible at the moment. For second I don't know any library at the moment therefore. But as Metro is based on simple combinations of rectangles and squares it is predestinated for grids.
Best regards,
mukarev