Hi Tsangan,
What I did in the past was use a piece of cloth and then sewn an elastic band on the bottom and then it works like a hair bonnet. I had one for my Model M. You can easily make any custom size and while it may not look as good as the acrylic roofs, it serves the purpose. To give credit where credit is due, it was my wife who did the sewing and it was her idea. This was after we bought the IBM PS/2 model 80 for big bucks and she wanted to protect the investment.