In the first photo you can see the sawed and drilled parts. These are made from a 4x4mm brass U-profile, available at Conrad, a 2mm brass tube, and some 1 x 12mm round head nails, both available at Hornbach.
Furthermore, you will need 1mm spring steel to drive the barrier with a servo and of course some paint.
In the photo, the parts are soldered together, sanded, and primed with an airbrush.