u/Imawapagiki

Hi there,
I will soon receive two unequal PVC L-angles which I intend to use to create blackout blinders for roller blinds in a bedroom. (The light bleeds out between the blind and the window architrave.) But the length I found is too long. How best to cut this kind of piece? Or where? I'm trying to find workshops in the area (London SE5) but coming up short...
Thanks!