If you want to build you own PC case, getting the measurements right can be difficult due to the tight tolerances.
This template should help you to position the holes for the mainboard standoffs correctly.

Update:

I added a second version with I/O shield alignment guide. The space between the two collumns marks the horizontal position of the I/O shield.
For the vertical position, the lower edge of the I/O cutout needs to be 2.24 mm below the mainboard. So hight of your MB standoffs - 2.24 mm = height above MB mounting surface.
The upper edge of the cutout should be 44.45 mm above the lower edge. (cutout should be 158.75 mm x 44.45 mm)

NOTE: I haven't testet this model yet, but since the measurements are based on a printable case I designed, which worked and was based on ATX specs, this should work too.