How to make a room using double sided shader and two image textures?

Hi i am having trouble trying to make my room model double sided so when i apply two image textures so one side is the outer wall and the other the inner wall. i tried to create a custom two-sided texture but not all the walls are two sided. Can anyone help me fix the issue?

the shader must use CULL OFF if you want to see both sides of a model’s face visible. you use VFACE to determine whether you’re looking at a front or back face and choose the texture with that.
the issue with this method, is that you’re always going to read two textures, unless you use a branch which can be very finnicky on whether they help or not, so i would just recommend having a front wall and a back wall, as in real life. 99% of games do this, so it’s kind of an indication that it’s the way to go.
i personally build all my levels in an editor that lets you create primitives/csg, so i just use a rectangular prism from the start, thus never having to think about making two sides of a wall. just don’t forget to remove any unseen/overlapping faces.

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