Pages 7.3 has some quite good drawing tools, but I recommend you use an accurate pdf instead.
If you still want to do this in Pages do it in a Layout mode (easier to select objects) document and copy it back to the WP document:
Make a rectangle shape > Style > Whatever line you want > No fill


Arrange: Stay on Page > Text Wrap > None

Do the same with a line and use Size, Rotate Angle & Position to start assembling your grid.
Holding down the command key will get a pointer.
Make copies of objects by option dragging them, small numbers then groups to buildup your grid.
In the top menu you can use Arrange > Align/Distribute Objects to arrange the parts.
When you are finished, group the lot, position the group, copy it over to WP document and send to back, lock it.