Thanks for the question. There's not actually a way to bevel corners of different widths at the moment without the effects shown in your screen capture. Instead, I would recommend letting the segments but up against one another like this:
To do that I'm controlling two padding values. The right padding of a Transform node wired to the Corner input. This pushes the first segment in a row along to account for the width of the previous wall.
To do this we take the Y Size from the Selector operator, divide it in half, and wire it to the Right Padding input.
The second padding value is the wall itself. This one is a negative value that extends the segment slightly past the corner to account for the width of the next wall.
To do this we'll export the width of both segments and wire them to an Arithmetic node. You can then use this expression: return if(XSplineNextMatID ==2, -Input2/2, -Input1/2);
Basicallly it picks the size based on the material ID of the next section of the spline. Once again we divide it by two and this time negate the value to extend the geometry past the corner.
A sample file is attached.
I hope that helps, please let me know if you have any further questions.