I want to make a window template for positioning in a wall to later fit a standard 1200mm x 1200mm window. does this mean the outer of the frame should be 1200mm x 1200mm thinking the 5-10mm gap around the window is already accounted for in the actual size of the window or are the windows 1200mm x 1200mm meaning the template needs to be 1210 mm x 1210mm. hopefully that is understandable and any help would be much appriciated.