yr_right, time to read up about Schedule 8.
Schedule 8:
Maintenance that may be carried out on a Class B aircraft by a pilot entitled to do so under subregulation 42ZC(4)
...
6. Replacement of side windows in an unpressurised aircraft.
Note that it does not say MANUFACTURE the window. An aircraft plastics place is the best to do that. A couple hundred dollars each.
Of course you have to put it in the log book. Same if you replace the battery.