sugestions on putting treated boards over cements? Reason being for morture problem.

I wouldn't use pressure treated lumber for that if you're planning to put any holes in that lumber for fastening it down or whatever. That's because it's only the exterior of pressure treated lumber that's rot resistant.

I'd probably use a wood composite decking material. Wood composite deck materials are a mixture of wood fiber and plastic resin that are mixed together and extruded into a shape similar to a hollow board. These kinds of materials don't absorb water and don't rot.

http://kurniacyber.com/wp-cont...omposite-decking.jpg

You should also be aware that there's probably a safety by-law requiring that all steps on a stairway be of equal height so that people don't get tripped up by uneven stair heights. So, you're going to probably have to add some pressure treated wood or wood composite deck material to your porch floor to ensure a uniform step heigh. How far onto your porch that elevated floor has to go is something I don't know.

Your going to have to go back and add a lot more detail, like what is it your really trying to do. A picture would be nice to.
Trying to figure out how you think adding pressure treated wood would do anything to waterproof steps.
If your thinking about installing some thing like pressure treated decking directly over any concrete, scratch that idea.
What will happen is the underside will get wet and as the top part starts to dry it will cup the wood, The underside will also start to rot out.
The screws will also work loose from all the expantion and contraction.