Since you are not doing the work. I will do it for you without the limited grid like snap in Win Metro.
1) Move your window with thick borders like Win95/98/ME/XP/Vista/7/8.
2) touch two vertical borders.
3) hover on the border, a super thick binder border will fade in quickly with a ring holes on both sides.
4) click on the either binder ring hole will now group the window as one. It will move together and when you resize the touching border, it will expand and shrink on the other side.
5) if you touch two vertical borders, and you aligned top border, you automatically match your top position and window height. (three rings holes on each sides will appear, one at touching border like #3 and another two are above and below #3, these bind both directions.)
6) if you touch two horizontal borders, and you aligned left border, you automatically match your left position and window width. (three rings holes on each sides will appear, one at touching border like #3 and another two are left and right of #3, these bind both directions.)
7) You can unbind by removing the binder ring.
This is far far far more flexible, just like PowerPoint. And a thick border still make windows separate nicely. And this does not limited to a grid. You can effectively snap by columns (by only doing 1~4 and no 5/6) and have free form in each column.
And I doubt your idea would top this.