I want do my own mesh "quad", but not square, I want a 2D polygon to apply in a parallax scroll

I need do a 2d polygon mesh, how can I do?
other option valid for me is generate mesh from image, not sprite renderer, mesh renderer, I want this for use the offset texture, Quad is so big, and my scroll images are with transparency, so is very space without use.

I do not want a quad, I want a polygon with the shape of the desired background, for example for a parallax scroll, I need to use quads backgrounds and those textures occupy a lot besides the cost for the gpu, I would like to make 2D meshs with the desired shape.