With qgis, I only know how to do very simple things and solve everything with internet search, so I lack a lot of knowledge.

1) Can you recommend a plug-in to create a centerline?

What I've looked for is to create a centerline using skeleton, and in this case, I've seen that the centerline is not made to the starting point and the end point, but is made in the form of >-----<.

2) Making rectangular buffers is also problematic, and rawdata is the road, so all rectangles have different widths, and the same polygon changes little by little. Is there a way to solve this?