S. Shaw see this link for many examples of filling beds, over soil that is full of weeds.
http://www.charlesdowding.co.uk/march-2013/
For most fillings of new beds I do not use cardboard.
I use cardboard mostly on paths, in the first year, to kill weeds. And not after that.
And a lot depends what materials you have available. There is no precise formula. Just keep your finest compost for the surface layer, to sow and plant into.
