To make your own version, start off by measuring the window and the space you want covered. (I like having a bit of light shining through the bottom, so I made my blind a bit shorter than the full window.)
Then cut the fabric to the appropriate size, adding an additional inch and a half of extra fabric at the top of the blind and the appropriate extra fabric at the sides depending on whether you are using pinking shears (the super easy way) or regular scissors with extra fabric (the easy way).
The magnets will go at the top so make sure you have enough space above the window with the fabric to do so.
Important Tip: If you are using a bold pattern, make sure it is centered how you want it before you cut the fabric.