What is the traditional way to layer a lasagna?
Traditionally, you start with a layer of pasta at the bottom, then go ragu-bechamel-lasagne-ragu-bechamel-lasagne, and finish with a layer of bechamel directly on top of the last pasta layer, followed by a liberal covering of grated parmesan. 

It is also common to add a sprinkling of parmesan on top of the bechamel in each layer. 

Ratios are subjective but I would say it is normal to have roughly twice as much ragu as bechamel