My printer came without the plastic oval windows. This project has two options. The first is a one-piece netted window to keep bugs out. The other option is a no-net window, plus a shim, that you can use to attach a piece of clear acrylic.
This is pretty heavily parametrizable if you want to use it in a different project/printer.
In the OpenSCAD file, set net_thickness=0 to print a window, and set only_shim=true to print the shim for holding the acrylic in place.