Translucent MIDBARS3 walls with set height

[Guest]

Hello. I am quite new to Doom mapping and I wanted to make map with a "railing" that has collision, is translucent and has a set height. I have no idea how to do such a thing, as my past attempts have resulted in a) a black texture instead of a translucent one; b) no collision.
The setup should look about like this:
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_______|_______
The ceiling is an F_SKY1, if that will help.

[snailatspace]

UPD: I am actually stupid, as I forgot to disable noclip.